-#^         ^  * 


m 


ELEMENTARY    EXPERIMENTS 

IN 

PSYCHOLOGY 


BY 


CARL   E.  SEASHORE 

W 
Bead  of  the  Department  of  Philosophy  and  Psychology  and  Bean  of  the 

Graduate  College  in  the  State  University  of  Iowa 


NEW  YORK 
HENRY  HOLT    AND    COMPANY 

1908 


PSYCH. 
LIBRARY 


•HAL 


Copyright,  1908, 

BY 

HENRY  HOLT  AND  COMPANY 


THE    QUINN    &    BODEN    CO.    PRESS 
RAHWAV,    N.    J. 


PEEFACE 

This  manual  is  designed  to  meet  the  requirements 
for  a  series  of  individual  experiments  in  the  first  course 
in  psychology.  It  makes  individual  experiments,  as 
opposed  to  class  demonstrations,  practicable,  regardless 
of  laboratory  facilities  or  the  size  of  the  class.  The 
student  is  given  means  and  encouragement  for  pursuing 
each  problem  intensively  in  order  that  he  may  acquire 
independence  of  thought  and  action,  realize  the  actual- 
ity of  mental  processes,  and  get  here  and  there  a  vision 
of  the  vastness,  the  orderliness,  the  practical  signifi- 
cance, and  the  charms  of  mental  life. 

'No  laboratory  facilities  are  required.  In  this  there 
is  a  triple  gain :  it  saves  the  manifolding  of  equipment, 
it  frees  the  student  from  the  technicalities  incidental 
to  the  manipulation  of  apparatus  at  a  time  when  his 
energies  need  to  be  conserved  for  the  grasping  of  the 
psychological  problem,  and  it  saves  time  for  the  class 
period,  the  experiments  being  adapted  for  outside  as- 
signments. The  apparatus  other  than  that  ordinarily 
at  the  disposal  of  students  is  supplied  with  the  book  in 
the  accompanying  envelope.* 

*  The  president  of  a  college  asked  a  distinguished  psychologist 
how  much  money  his  board  ought  to  appropriate  for  the  equip- 
ment of  a  fair  elementary  laboratory.  The  reply  came:  "Three 
thousand  dollars  a  year  for  a  good  instructor  and  one  dollar 
for  paper  and  pins."  This  manual  supplies  the  paper  and  pins 
and,  in  part,  the  instructor. 

iii 

178214 


iv  PEEFACE 

The  experiments  are  independent  and  self-explana- 
tory. Provided  the  manual  is  used  in  connection  with 
the  customary  elementary  text-book  or  lectures,  the 
experiments  require  no  introduction ;  the  directions  are 
adequate,  and  the  running  comment  furnishes  the  set- 
ting for  each  step  and  enables  the  student  to  see  the 
significance  of  the  results.  The  beginner  needs  much 
help  in  his  experiments  in  psychology,  and  there  is  no 
more  practical  way  of  giving  it  than  through  a  manual. 

This  is  not  a  laboratory  manual.  It  is  a  manual  of 
experiments  which  the  student  should  perform  before 
he  is  admitted  to  the  laboratory,  or  in  case  he  does  not 
intend  to  pursue  the  subject  beyond  one  course.  It  is 
not  a  text-book  by  itself,  but  a  supplement  to  any  good 
text-book.  It  does  not  review  the  field  of  psychology,  but 
simply  furnishes  the  intensive,  individual,  experimental 
part  of  the  instruction.  It  does  not  furnish  technical  in- 
struction on  methods  of  experimenting,  but,  like  the 
conversational  method  of  teaching  language,  everywhere 
encourages  right  procedure.  It  does  not  purport  to 
cover  the  most  important  matters ;  sometimes  an  almost 
insignificant  topic  (for  example,  the  subject  of  the  first 
chapter)  is  chosen  for  the  purpose  of  deepening  insight. 
It  by  no  means  supplants  the  class  demonstrations  and 
experiments,  except  in  the  few  topics  selected,  and  even 
here  the  instructor  may  profitably  supplement  and  show 
how  the  same  experiments  may  be  performed  by  the 
usual  laboratory  apparatus. 

The  manual  presupposes  such  knowledge  of  the  nerv- 
ous system  ^s  is  imparted  by  the  text-books  most  used  in 
psychology.     It  aims  to  retain  the  most  generally  ac- 


PREFACE  V 

cepted  classifications  and  terms,  to  introduce  those  ex- 
p.eriments  which  have  come  into  most  general  favor, 
and  to  leave  untouched  those  fields  in  which  experiment 
has  been  of  doubtful  value.  The  discussion  on  each 
topic  is  limited  to  the  bearings  of  the  experiment. 

As  to  the  method  of  using  the  book,  each  instructor 
will  naturally  adopt  that  best  suited  to  his  situation. 
If  space  is  available,  the  students  should  be  encouraged 
to  perform  the  experiments  in  the  roojns  of  the  depart- 
ment during  certain  open  hours,  and  under  the  general 
supervision  of  an  assistant.  There  should  be  sufficient 
time  allowed  in  the  recitation-period  for  special  sug- 
gestions and  directions  to  the  students,  and  for  reports 
upon  the  completed  experiment.  The  students'  notes 
on  each  topic  must  be  collected  and  checked  rigorously ; 
for,  no  matter  how  explicit  the  directions  may  be,  the 
quality  of  the  work  must  be  passed  upon  by  the  instruc- 
tor. It  is  profitable  to  require  the  students  to  take 
turns  in  working  over  the  reports  to  show  difficulties, 
original  observations,  special  demonstrations,  etc.  Or- 
dinarily each  experiment  will  take  two  hours.  The 
first  experiment  should  be  divided  into  two  assignments, 
on  account  of  the  newness  of  the  work  and  in  order 
to  avoid  fatigue. 

Titchener's  monumental  four-volume  set  of  labora- 
tory manuals  is  a  most  valuable  compendium.*  It 
contains  bibliographies,  besides  technical  discussions  of 
nearly  every  topic  in  this  course.      Sanford's,t  Wit- 

*Titehener,  "Experimental  Psychology":  Qualitative  (I)  Stu- 
dent's Manual  and  (II)  Instructor's  Manual;  Quantitative '(III) 
Student's  Manual  and    (IV)    Instructor's  Manual. 

f  Sanford,  "Experimental  Psychology." 


vi  PREFACE 

mer's,*  and  Judd'st  manuals  are  helpful  references. 
Baldwin's  dictionary  of  Philosophy  and  Psychology 
should  also  be  on  the  reference-table,  together  with  the 
most  approved  elementary  texts. 

The  author  has  gleaned  material  from  many  sources 
and  wishes  here  to  acknowledge  his  gTateful  obligations 
to  those  who  find  themselves  contributors  to  this  volume. 
He  has  had  the  benefit  of  helpful  advice  from  many 
psychologists  of  experience ;  several  of  them  have  kindly 
read  the  manuscript  and  made  valuable  suggestions. 
He  is  especially  indebted  to  his  colleague  Dr.  Mabel 
Clare  Williams  for  cooperation. 

*Witmer,  "Analytical  Psychologj\" 

f  Judd,  "Laboratory   Manual   of   Psychology"   and  "Laboratory 
Equipment  for  Psychological   Experiments." 


CONTENTS 


Preface 
Introduction 
I.     Visual  After-Images 
II.     Visual  Contrast 

III.  The  Visual  Field 

IV.  Visual  Space 

V.     Auditory  Space  . 
VI.     Tactual  Space 
VII.     Cutaneous  Sensations 
VIII.     Weber's  Law 
IX.     Mental  Images    . 
X.    -Association    . 
XI.  '  Memory  .^    . 
XII.     Apperception 

XIII.  Attention 

XIV.  NoRMAX  Illusions 
XV.     Affective  Tone  . 

XVI.    Reaction-Time 


PAGE 

iii 

ix 

1 

13 

23 

39 

55 

71 

82 

91 

104 

118 

131 

144 

158 

172 

191 

205 


vii 


INTEODUCTIOK 

To  the  Student: 

Psychology  is  a  systematic  study  of  mental  life. 
You  now  turn  from  the  study  of  physical  forces,  rocks, 
flowers,  and  animal  tissues,  in  nature  without,  to  a  study 
of  your  own  mind.  You  are  to  perform  experiments 
upon  yourself. 

The  experimental  method  enables  you  to  analyze  and 
reduce  a  mental  process  to  its  simplest  elements;  to 
control,  repeat,  and  vary  the  conditions  systematically; 
to  record  the  results;  to  trace  interrelations  and  ex- 
planations of  known  phenomena;  and  to  discover  new 
facts  and  problems. 

This  manual  is  so  arranged  as  to  furnish  set  exer- 
cises in  which  directions,  aids,  and  explanations  are 
given  in  the  order  needed.  Onl}^  a  few  of  the  most 
general  suggestions  for  your  guidance  need  be  given 
here. 

Finish  as  you  go  along.  The  paragraph  is  the  unit ; 
always  read  a  paragraph  at  a  time  and  perform  the 
experiment,  write  the  report,  or  master  the  explanation 
before  you  read  the  next.  This  is  mandatory,  because 
glancing  ahead  would  often  vitiate  the  experiment. 

Take  systematic  notes.  The  directions  for  notes  are 
specific  in  certain  minimum  requirements.  These  notes 
are  not  primarily  for  the  information  of  the  instructor, 
or  for  reviews  and  examinations,  but  for  the  purpose 


X  INTRODUCTION 

of  clinching  the  observed  facts  and  gaining  practice  in 
the  recording  of  the  results,  which  is  an  essential  step  in 
an  experiment.  Use  loose-leaf  note-books ;  hand  in  the 
report  for  each  experiment  to  the  instructor  for  inspec- 
tion ;  and  file  the  notes  as  they  are  returned. 

Work  intensively.  Seek  the  most  thorough  insight 
into  the  problem  under  consideration ;  note  new  observa- 
tions, test  ideas  suggested  to  you,  verify  and  check  as 
much  as  time  permits.  Reason,  and  thus  develop  con- 
fidence in  your  own  judgment  and  power  of  observation. 
But  always  adhere  to  the  set  tojoic.  Do  not  ramble,  or 
follow  up  the  countless  fascinating  side  lines  which 
come  to  view.  Follow  the  directions  closely,  then 
develop  your  original  ideas. 

Apply  what  you  learn.  You  will  learn,  for  example, 
many  laws  of  mental  economy  in  this  course.  When 
you  have  discovered  and  demonstrated  such  laws,  use 
them.  Economize  mental  energy !  Psychologize  in 
your  history  lesson,  your  literature,  your  material 
science,  your  athletics, — wherever  you  are  concerned 
with  mental  processes.  To  educate,  to  heal,  to  govern, 
to  please,  to  interpret  the  efforts  and  j)roducts  of  the 
human  mind;  to  understand  inclinations,  proclivities, 
and  capacities  of  your  own  and  other  minds,  involves 
knowdedge  of  mind,  which  is  psychology."^ 

*  "Only  with  the  aid  of  psychology  can  one  to  the  fullest 
possible  extent  reap  the  benefits  of  the  study  of  other  forms 
of  science.  Language  cannot  be  understood,  literature  cannot 
be  appreciated,  read,  and  interpreted,  art  cannot  be  profoundly 
comprehended,  and  even  the  natural  sciences  cannot  have  their 
full  import  revealed,  without  a  knowledge  of  the  mind  of  man. 
And,  indeed,  how  could  this  be  otlierwise,  since  all  science  itself 
is  only  the  product  of  the  human  mind?"      (Ladd.) 


INTRODUCTION  xi 

Be  impartial:  be  not  self-centered.  You  will  be 
called  upon  to  exhibit  and  measure  your  mental  capaci- 
ties in  various  ways,  and  it  requires  the  integrity  and 
courage  of  a  scientist  to  observe  and  report  these  with- 
out bias. 

Go  only  as  far  in  an  assignment  as  you  can  go  thor- 
oughly. One  student  may  be  able  to  proceed  two  or 
three  times  as  fast  as  another.  If  you  find  that  the 
lesson  is  too  long  for  you,  do  not  skim  over  any  part, 
but  proceed  as  far  as  you  can  and  record  the  time  limit. 

In  the  experiments  that  follow,  'Tor  one"  means  that 
the  experiments  so  headed  may  be  performed  by  one 
person  alone.  'Tor  two"  means  that  two  must  work 
together,  one  acting  as  experimenter  (E)  and  the  other 
as  observer  (O).  Shift  in  each  experiment  so  that 
each  one  may  serve  in  turn  both  as  experimenter  and 
as  observer.  Record  which  one  served  as  observer  first. 
Each  should  keep  the  notes  which  naturally  go  into  his 
book  according  to  the  directions.  Record  also  the  date, 
the  hour  of  the  beginning  of  the  experiment,  interrup- 
tions, and  any  general  conditions  which  might  influence 
the  results.     Use  terse  language. 

To  experiment  is  to  ask  questions  of  nature.  Do  not 
simply  repeat  the  set  questions  of  the  book,  but  let  them 
open  deeper  and  more  serviceable  inquiries  into  your 
mental  nature.  Your  primary  aim  in  this  course  should 
be,  not  to  collect  facts,  but  to  acquire  training.  Carry 
habits  of  introspection,  precision,  analysis,  and  natural 
explanation  into  life  and  you  will  realize  the  force  of 
our  motto :    'Not  psychology,  but  to  psychologize. 


CHAPTEE  I 
VISUAL    AFTER-IMAGES 

For  One* 
Most  of  us  have  observed  that,  if  we  look  for  a  mo- 
ment at  a  liglit  as  it  is  being  turned  out,  we  see  an 
image  of  it  a  while  afterward.  That  image  is  an  after- 
image, or  after-sensation.  Such  images  manifest  them- 
selves according  to  traceable  laws  and  play  an  im- 
portant, though  seldom  recog-nized,  role  in  our  experi- 
ence. We  shall  now  make  a  study  of  some  of  their 
characteristic  modes  of  behavior. 

Success  in  this  experiment  depends  mainly  upon 
concentration  of  attention  and  economy  in  the  use  of 
the  eyes.  The  eyes  should  not  be  allowed  to  wander 
aimlessly  over  the  figures,  and  it  is  well  to  close  them 
for  rest  as  often  as  possible.  Clear  images  can  be 
obtained  only  after  steady  fixation.  It  is  easier  to  get 
the  after-image  with  one  eye  alone,  but  in  the  long  run 
it  is  more  restful  to  use  the  two  eyes  together. 

1.  Existence,  a.  Brightness. — Place  the  black  square 
at  the  center  of  the  upper  half  of  a  white  sheet  of 
paper;  fixate  the  center  of  it   (i.e.,  look  intently  and 

*Take  from  the  envelope  the  large  black  and  gray  squares,  and 
the  following  small  squares:  black,  gray,  white,  red,  blue,  yellow, 
green,  violet,  and  orange.  Make  a  pinhole  at  the  center  of  each 
of  these  squares.  ♦ 

1 


2  VISUAL  AFTEK-IMAGES 

steadily  at  the  pinhole)  for  about  fifteen  seconds ; "'  then 
look  at  the  center  of  the  lower  half  of  the  sheet  of  white 
paper  and  you  Avill  see  a  bright  square,  which  is  the 
after-image.  Record  your  estimate  of  its  relative  size 
and  duration. 

h.  Color. — Try  the  red  square  in  the  same  manner. 
Record  the  color  of  the  after-image. 

An  after-image  is  a  sensory  image  which  occurs  as 
the  result  of  the  stimulation  of  a  sense-organ  but 
not  until  after  the  stimulus  has  been  withdrawn.  It 
is  a  sort  of  echo  and  bears  certain  relations  to  the  ob- 
ject of  which  it  is  a  copy  as  regards  space,  duration  of 
the  primary  impression,  sense  quality,  and  intensity. 
Thus,  in  this  experiment,  you  saw,  on  the  surface  of 
the  blank  paper,  copies  of  the  squares  possibly  like  the 
original  in  every  respect  except  brightnesst  and  color. 
After-images  combine  certain  characteristics  of  sensa- 
tions and  mental  images  and  might  equally  well  be 
called  after-sensations. 

The  causes  of  after-images  are  present  in  all  our 
vision  and  tend  to  modify  practically  all  that  we  see. 
Yet  many  persons  live  long  and  happily  Avithout  making 
allowance  for  their  distortions  or  even  discovering  the 
existence  of  them.  Every  object  that  we  see  leaves  an 
impression  which  may  bob  up  as  an  after-image,  if  suf- 
ficiently strong  and  isolated.  We  look  at  a  piece  of 
black   paper    and   the    next   moment    we    see    a    copy 

*  A  fixation-time  of  fifteen  seconds  is  too  long  for  some  and 
too  short  for  other  observers;  each  will  soon  determine  what 
time  is  most  favorable  for  his  eyes. 

f  Black,  white,  and  all  the  intervening  grays  are  called  bright- 
nesses.    Brightness  is  also  present  in  color. 


VISUAL  AFTEE-IMAGES  3 

of  it  wherever  we  cast  our  eyes ;  the  same  is  true  about 
a  light,  a  color,  an  apple,  a  man,  a  tree,  a  book,  a  house — 
any  object  which  may  impress  the  eye.  The  after- 
images in  themselves  are  not  useful,  and  it  is  fortunate 
that  we  have  the  instinctive  power  to  disregard  them 
as  effectively  as  we  do.  But  even  though  we  disregard 
them,  they  modify  our  sensory  experience  and  con- 
tinually tone  the  colors,  lights,  and  shades  of  our  en- 
vironment. 

After-images  occur  in  all  the  senses,  but  the  visual 
are  the  most  consjDicuous. 

2.  Setting. — Eepeat  Exp.  1  a  and  observe  that,  when 
the  light  after-image  appears,  there  is  a  change  in  the 
white  surface  surrounding  it.*    Describe  the  change. 

When  we  look  at  an  object  we  may  secure  an  after- 
image not  only  of  that  object  but  also  of  its  surround- 
ings within  a  limited  field  of  vision.  This  complexity 
of  the  impression  is  one  of  the  reasons  why  specific 
after-images  are  so  difficult  to  detect  and  so  easy  to 
disregard. 

After-images  are  local  effects  of  the  adaptation  of 
the  eye  to  changes  in  brightness  and  color.  When  we 
enter  a  dark  room,  it  seems  at  first  intensely  dark,  but 
later  it  assumes  gray  or  color  effects.  When  we  pass 
from  a  dark  into  a  light  room,  the  light  at  first  is  daz- 
zling, but  the  eye  soon  adapts  itself  so  that  after  a 
while  the  light  does  not  seem  so  bright.  During 
adaptation  all  brightnesses  and  all  colors  tend  toward 

*  If  the  white  sheet  is  placed  against  a  dark  background,  the 
outline  of  the  whole  sheet  may  be  seen  in  the  after-image. 


4  VISUAL  AFTER-IMAGES 

gray.  In  the  above  experiment  a  square  portion  of  the 
retina  is  adapted  to  dark  and  the  surrounding  portion 
to  light. 

3.  Color. — In  successive  trials,  produce  after-images 
of  the  five  colors,  blue,  green,  yellow,  violet,  and  orange. 
Record  the  dominating  color  in  each  after-image.*  Cau 
you  formulate  a  law  for  this  order  of  color?  If  so, 
state  it. 

The  after-image  of  any  color  goes  through  a  series 
of  rapid  changes,  possibly  covering  the  whole  spectrum ; 
but  there  is  always  one  particular  color  which  dom- 
inates by  being  the  most  distinct  and  by  persisting  the 
longest.  This  color  is  complementary  to  the  color  of  the 
stimulus,  t  Of  course  it  is  modified,  according  to  cer- 
tain laws,  by  the  color  and  the  brightness  of  the  back- 
ground upon  which  it  is  projected. 

The  after-image  of  the  dark  stimulus  in  the  first 
experiment  was  light;  that  is,  antagonistic.  We  may 
therefore  combine  the  observations  on  brightness  and 
on  color  and  say  that  the  dominant  color  and  brightness 
of  an  after-image  are  antagonistic  to  the  color  and 
brightness  of  the  stimulus.  All  color  after-images  also 
involve  brightness-effects.  Colors  are  often  seen  in  the 
after-images  of  non-colored  objects. 

4.  Projection-background,  a.  Brightness-effect  on 
Brightness. — Repeat  Exp.   1  a  in  six  successive  trials 

*  Do  not  try  these  in  too  rapid  succession ;  it  may  be  well  to 
intersperse  them  with  following  experiments.  Beware  of  look- 
ing at  the  colors  out  of  mere  curiosity  or  aimlessness! 

f  Every  color  has  a  complementary,  i.e.,  an  opposite  or  antag- 
onistic color.  Colors  are  said  to  be  complementary  if  they 
neutralize  each  other  and  produce  gray  when  mixed. 


VISUAL  AFTER-IMAGES  6 

under  uniform  conditions,  except  that  you  project  the 
image  upon  different  backgrounds ;  ^  namely,  white, 
gray,  and  black,  in  the  double-fatigue  order. f  Record 
the  relative  effectiveness  of  the  three  backgrounds. 

The  clearness  of  an  image  depends  upon  the  bright- 
ness-difference between  it  and  its  projection-back- 
ground. When  projected  upon  the  white  ground,  in  this 
experiment,  the  light  of  the  image  is  intensified  and 
the  darkness  of  the  surroundings  is  reduced  by  the 
white;  on  the  black  ground,  the  light  of  the  image  is 
minimized  and  the  darkness  of  the  surroundings  is 
enhanced  by  the  black;  while,  on  the  gray,  there  is  a 
moderate  interference  with  both  image  and  surround- 
ings. Hence  brightness  of  the  background  makes  com- 
paratively little  difference  in  the  effectiveness  of  the 
after-image,  although  the  brightness  of  the  three  images 
varies  greatly.  For  a  dark  object  the  white  projection- 
background  is,  however,  usually  more  effective,  because 
here  the  white  enhances  the  image  of  the  object  itself, 
whereas  on  a  black  projection-background  it  is  the  back- 
ground of  the  object  that  is  enhanced. 

h.  Brightness-effect  on  Color. — Repeat  Exp.  1  &  in 
three  successive  trials,  projecting  the  image  upon  white, 
gray,  and  black  backgrounds  respectively.  Record  the 
effect  of  the  background  upon  the  color  of  the  after- 


*Use  the  two  large  squares  for  gray  and  black  projeetion-back- 
grovmds. 

■f  Double- fatigue  order  is  the  technical  term  for  the  giving  of 
a  series  of  trials  in  one  order  and  repeating  them  in  the  reverse 
order;  thus,  white,  gray,  black;  black,  gray,  white.  The  theory 
is  that  such  factors  as  fatigue  and  practice  tend  to  even  up  by 
this  order. 


6  VISUAL  AFTER-IMAGES 

There  is  a  distinct  effect  upon  the  brightness  of  the 
color;  the  actual  color  of  the  image  mixes  with  the 
brightness  of  the  background. 

c.  Color-effect  on  Color. — Project  the  after-image 
of  the  red  square,  in  successive  trials,  upon  the  yellow, 
the  blue,  and  the  red  square  itself.  Record  the  result- 
ing color-effects. 

The  color  of  the  after-image  mixes  with  the  color 
of  the  background.  Thus,  the  result  on  the  yellow  is  a 
greenish  yellow;  on  the  blue,  a  greenish  blue;  and  on 
the  red  a  tendency  toward  gray.  This  last  trial — red 
upon  red — explains  why  colors  change  and  blur  when 
we  look  intently  at  them;  the  after-image  of  the  red 
disk  is  a  pale  green,  and  if  it  were  projected  upon  a 
pale  red  of  the  same  strength,  the  result  would  be 
to  cancel  both  colors,  according  to  the  law  of  comple- 
mentaries. 

d.  Absence  of  BacJcground. — Fixate  the  black  square 
as  before,  and  then  put  your  hands  over  your  eyes  and 
you  will  see  the  image  projected  somewhere  into  space.* 
Record  your  estimate  of  its  size  and  distance  and  the 
relative  effectiveness  of  this  and  the  foregoing  modes  of 
projection. 

The  image  may  be  projected  anywhere — upon  any 
color  or  brightness,  upon  any  form,  at  any  distance 
within  sight.  A  glance  at  the  setting  sun  produces 
shifting  color-effects  upon  the  object  we  look  at  imme- 
diately afterward ;  the  after-image  of  the  green  leaf  in 

*  It  is  usually  better  to  keep  the  eyes  open  when  covered  by 
the  hands;  still,  it  makes  but  little  difference  whether  they  are 
open  or  closed,  provided  the  covering  is  adequate. 


VISUAL  AFTEE-IMAGES  7 

a  woman's  hat  may  be  taken  for  a  rosy  blush  upon 
her  cheek. 

5.  Negative  and  Positive. — Look  at  a  lighted  lamp  * 
for  half  a  second,  and  then  instantly  cover  the  eyes  and 
observe  the  radical  changes  in  color  of  the  after-image. 
Record  the  two  dominant  colors  in  the  order  of  their 
appearance,  t 

The  positive  after-image  has  the  same  relations  of 
brightness  as  the  stimulus,  as  in  a  photographic  positive. 
The  negative  after-image  has  the  relations  of  light 
and  shade  reversed,  as  in  the  photographic  negative. 
The  after-image  may  be  of  the  same  color  as  the 
stimulus,  or  it  may  be  other-colored.  There  are 
positive  same-colored  and  positive  other-colored,  nega- 
tive same-colored  and  negative  other-colored  after- 
images. Generally,  however,  positive  after-images 
are  same-colored  and  negative  other-colored  are  com- 
plementary. 

The  positive  after-image  appears  first  and  is  usually 
very  short  in  duration  and  difficult  to  detect.  To  make 
it  conspicuous,  one  must  employ  a  strong  stimulus,  as 
in  this  experiment.  After  some  training  one  may  see 
the  positive  after-image  before  the  negative  in  the  ex- 
posure of  ordinary  objects  of  moderate  intensity. 

*Any  kind:   daylight  does  not  interfere  seriously. 

•j-  Positive  after-images  of  brightness  without  color  may  be  dem- 
onstrated as  follows:  Face  some  distant  object,  as  the  branching 
limb  of  a  tree  outlined  against  a  clear  sky;  close  the  eyes  and 
cover  with  the  hands  for  a  minute;  then  open  the  hands  and 
eyes  for  a  fraction  of  a  second,  and  observe,  immediately  after 
closing  the  eyes  again,  an  image  like  the  object  in  brightnesSc 
This  is  the  positive  after-image. 


8  VISUAL  AFTEK-IMAGES 

6.  Size  and  Distance. — In  three  successive  trials 
project  an  after-image  of  the  black  square,  as  in  Exp.  1  a, 
upon  backgrounds  at  different  distances  from  the  eye ; 
e.g.,  1  ft.,  3  ft.,  and  10  ft.  Formulate  a  law  of  the 
relation  between  size  and  distance. 

This  variation  of  the  size  with  distance  shows  that 
the  after-image  follows  the  same  optical  principles  of 
projection  as  the  normal  retinal  image  in  perception. 

7.  Relief. — Project  an  after-image  of  a  hat,  a  lamp- 
globe,  or  any  other  object  that  presents  relief  or  volume. 
Is  there  any  suggestion  of  relief  or  volume  in  the  after- 
image ? 

The  perception  of  relief  depends  upon  the  differences 
between  the  images  in  the  two  eyes,  delicate  gradations 
in  brightness,  and  eye-movements,  among  other  data. 
The  blurred  edges,  the  reversal  of  brightness,  and  the 
confusion  of  eye-muscle  sensations  militate  against  the 
perceptions  of  relief  in  the  after-image.  Ordinarily 
the  after-image  presents  only  the  outline  and  does  not 
suggest  relief,  but  training  and  care  may  enable  one 
to  identify  marks  of  relief. 

8.  Plasticity. — Project  an  after-image  of  the  black 
square  into  an  upper  corner  of  the  room.  Record 
whether  the  image  adapts  itself  to  the  ceiling  and  wall- 
surfaces,  or  retains  its  flat  form. 

It  may  do  either;  which  it  shall  do  is  a  matter  of 
apperception.  Usually  it  adapts  itself  plastically  to  the 
surfaces.  This  is  particularly  true  if  the  image  is  pro- 
jected upon  some  familiar  surface,  as  the  sleeve  or  the 
hand. 


VISUAL  AFTEE-IMAGES  9 

9.  Movement. — Fixate  the  black  square,  as  in  Exp.  1 
a,  and  project  the  image  with  eyes  closed  and  covered 
by  the  hands,  and  try  to  keep  the  after-image  directly 
before  you.  Does  the  image  seem  to  move  irresistibly  ? 
If  so,  in  what  direction  ? 

It  is  clear  by  this  time  that  the  after-image  moves 
mth  the  eyes ;  with  the  eyes  open,  we  see  it  in  whatever 
direction  we  look.  But  when  the  eyes  are  closed,  and 
we  are  not  aware  of  their  movement,  most  observers 
find  that  the  image  has  a  curiously  irresistible  tendency 
to  move  upward. 

10.  Latent   Period,    Duration,   and   Clearness. — In 

each  of  the  following  four  experiments  record  (1)  the 
approximate  latent  time,*  (2)  duration,  and  (3)  rela- 
tive clearness. 

a.  Time. — Project  the  after-image  of  the  black 
square  first  after  a  fixation  of  five  seconds  and  then 
after  a  fixation  of  ten  seconds,t  allowing  due  time  for 
recovery  between  the  two. 

h.  Brightness. — Place  the  black  and  the  gray  squares 
edge  to  edge  upon  the  white  sheet ;  fixate  the  adjoining 
edges  and  project  the  double  image  upon  a  white  back- 
ground. 

c.  Color. — Place  the  red,  the  green,  the  yellow,  and 
the  blue  squares  in  a  cluster  upon  the  white  sheet ;  mark 


*  The  latent  time  of  an  after-image  is  the  time  which  elapses 
between  the  withdrawal  of  the  stimulus  and  the  beginning  of 
the  appearance  of  the  after-image. 

f  This  time  should  be  adapted  to  the  individual  needs,  the 
requirement  being  that  a  relatively  short  exposure-time  shall  be 
compared  with  a  longer  one. 


10  VISUAL  AFTER-IMAGES 

a  point  in  the  center  of  the  cluster;  fixate  the  central 
point  and  project  the  four-colored  after-image  upon  a 
white  background. 

d.  Area. — Cut  a  piece  of  white  paper  about  eight 
millimeters  square  and  place  it  and  the  white  square 
five  millimeters  apart  upon  the  large  black  square ;  fix- 
ate a  middle  point  and  project  the  double  image  upon  a 
white  backgi^ound.* 

Long  stimulation,  large  brightness-diiference  between 
the  object  and  its  background,  and  a  moderately  large 
area  are  conducive  to  a  short  latent  time,  long  duration, 
and  clearness  of  the  after-image,  t  These  laws  are, 
however,  subject  to  numerous  qualifications. 

These  experiments  merely  show  how  it  is  possible 
to  work  out  laws  of  the  relation  between  stimuli  and 
after-images.:}:  The  rule  is  to  study  one  factor  at  a  time 
and  keep  all  other  conditions  constant.  The  factor 
which  is  studied  may  be  varied,  as  in  the  above  separat- 
ing of  time,  brightness,  and  area  under  controllable 
conditions,  and  the  effect  of  such  variations  may  be 
measured. 

The  certainty  that  the  image  shall  appear  depends 
mainly  upon  the  exposure-time,  the  area,  and  the  bright- 
ness of  the  stimulus,  but  also  upon  such  subjective  con- 
ditions as  are  mentioned  in  the  following  paragTaph. 

*  A  millimeter  scale  is  printed  on  the  last  page  of  this  book. 
Fold  the  margin  of  that  page  so  as  to  bring  the  scale  marking 
to  the  edge  of  the  page. 

f  The  variations  with  color  are  perhaps  essentially  due  to  the 
difference  in  the  brightness  of  the  color.  For  this  reason  blue 
is  the  most  effective  color  in   this  group  on  a  white  background. 

\  See  Franz,  "After-images,"  The  Psychological  Review  Mono- 
graph Supplement,  Vol.  Ill,  No,  12. 


VISUAL  AFTER-IMAGES  11 

If  any  one  of  these  is  inadequate  the  image  fails  to 
appear.  As  a  rule,  the  after-image  may  be  produced 
if  the  object  is  presented  utider  such  conditions  as  to 
be  clearly  perceptible.  Thus,  an  electric  spark,  which 
endures  only  for  an  infinitesimal  part  of  a  second,  may 
produce  an  after-image ;  in  the  present  experiments  the 
observer  may  not  have  noticed  the  after-image  of  the 
white  seen  through  the  pinhole,  but  objects  of  that  size 
may  produce  after-images  under  favorable  conditions; 
and  one  may  not  be  able  to  get  a  distinct  image  of  a 
white  plate  upon  a  white  tablecloth  because  the  bright- 
ness-difference is  too  small. 

The  duration  of  the  after-image  varies  within  wide 
limits.  In  extreme  cases  the  impression  has  been  known 
to  persist  for  days  and  months,  as  with  l^ewton,  who 
looked  at  the  sun  Avith  his  right  eye  and  then  saw  the 
sun  continually  before  him  for  many  days.  The  ordi- 
nary duration  is,  however,  limited  to  a  few  seconds, 
and  the  image  passes  away  gradually.  In  addition  to 
such  objective  conditions  as  exposure-time,  area,  and 
brightness  which  we  have  noted,  there  are  subjective 
factors,  such  as  practice,  expectation,  attention,  etc., 
which  condition  the  duration. 

11.  Indirect  Vision. — Fixate  a  point  about  seven 
centimeters  away  from  the  center  of  the  back  square ;  it 
then  stimulates  the  indirect  field  of  the  retina.  Project 
the  after-image.  Compare  the  effectiveness  of  this 
image  with  the  foregoing  images  from  the  direct  field. 

The  best  after-images  are  obtained  from  the  center 
of  the  retina.     Clearness  and  duration  gradually  de- 


12  VISUAL  AFTER-IMAGES 

crease  toAvard  the  periphery,  and  it  is  very  difficult  to 
get  any  image  from  the  extreme  periphery  of  the  retina. 
In  this  respect  the  after-image  behaves  like  the  primary 
image  in  perception. 

12.  Periodicity. — Fixate  the  black  square  nntil  it 
begins  to  blur  and  then  project  the  after-image  in  the 
most  favorable  way,  and  observe  that  it  recurs  again  and 
again.    Record  the  number  of  appearances. 

Under  favorable  circumstances  the  image  may  appear 
twenty  or  thirty  times.  This  periodic  recurrence  is 
a  fundamental  law.  Sometimes  the  usual  sequence  of 
positive  and  negative  phases  may  be  observed  in  each 
period. 

The  cause  of  after-images  lies  chiefly  in  the  fact  that, 
as  soon  as  a  light  stimulus  ceases  to  act  upon  a  given 
portion  of  the  retina,  a  reaction  of  the  chemicallj^  antag- 
onistic sort  follows.  The  play  of  the  after-image  in  all 
its  transitions  through  brightness  and  color  follows  the 
course  of  this  reaction  in  the  retinal  elements.* 

*  A  good  account  of  the  principal  plwsiological  theories  of 
color-vision  is  found  in  Calkins,  "Introduction  to  Psychology," 
pp.  464-79. 


CHAPTER  II 
VISUAL  CONTRAST 

For  One* 
Every  sensation  is  different  from  what  it  would  have 
been  if  it  had  been  experienced  together  with,  or  in 
sequence  to,  some  other  sensation.  One  of  the  best  illus- 
trations of  this  '^law  of  relativity"  is  to  be  found  in 
contrast,  which  we  shall  now  study  in  the  sense  of 
sight. 

These  experiments  should  be  performed  in  good  dif- 
fused daylight.  Unless  otherwise  directed,  the  object 
must  invariably  be  viewed  through  the  tissue-paper. 
The  foregoing  exercise  has  taught  the  importance  of 
avoiding  fatigue  for  color  and  brightness.  Make 
prompt  judgments  and  avoid  unnecessary  exposure  of 
the  eyes  to  the  figures. 

1.  Brightness-contrast. — Lay  the  black  and  the 
white  squares  about  three  centimeters  apart  uj)on  the 
background;  place  a  gray  bar  upon  each  of  them  and 
cover  the  whole  with  the  tissue-paper.     Compare  the 

*Take  all  the  small  squares  from  the  envelope.  Cut  two  bars 
from  the  small  gray  square  and  two  from  the  pale  green  square 
each  5  millimeters  wide.  Use  tlie  page  at  the  end  of  the  book 
containing  the  millimeter  scale  for  a  background,  and  cover  the 
colors  laid  upon  it  with  the  facing  sheet  of  tissue-paper. 

13 


14  VISUAL  CONTRAST 

brightness  of  the  two  gray  bars  and  record  which  is  the 
brighter. 

The  two  gray  bars  are  exactly  alike  in  brightness; 
but,  by  contrast  with  their  backgrounds,  one  becomes  a 
light  gray  and  the  other  a  dark  gray. 

There  are  two  kinds  of  contrast,  successive  and  sim- 
ultaneous. Successive  contrast  is  in  many  respects 
synonymous  with  after-images,  and  may  be  defined  as 
''the  apparent  alteration  of  a  gray  or  a  colored  surface 
by  the  previous  stimulation  of  the  same  retinal  area 
by  some  other  sort  of  light."  (Sanford.)  Simul- 
taneous contrast,  the  theme  of  the  present  chapter,  is 
described  as  ''the  mutual  effects  in  respect  to  color  and 
brightness  which  simultaneously  seen  but  separated 
visual  areas  have  upon  each  other."  (Baldwin.)  The 
difference  between  the  two  kinds  of  contrast  lies  in  the 
fact  that  one  is  due  to  successive  impressions,  whereas 
the  other  is  due  to  simultaneous  impressions.  The 
effects  of  the  two  kinds  of  contrast  are  closely  related. 

Consider  for  a  moment  the  practical  consequences 
of  the  phenomenon  just  demonstrated.  Wherever  sur- 
faces of  different  brightness  are  seen  together,  each 
modifies  the  brightness  of  the  other.  To  see  the  world 
of  lights  and  shades  as  it  really  is,  to  guide  ourselves 
accurately  in  seeing  form,  relief,  and  distance,  and  to 
be  able  to  make  the  proper  correction  wherever  contrast 
operates,  we  must  carry  in  our  minds  an  idea  of  the 
magnitude  and  a  knowledge  of  the  laws  of  brightness- 
contrast.  Contrast  is  both  helpful  and  deceptive ;  it 
magnifies  differences  and  therefore  often  helps  in  dis- 
tinguishing surfaces;    on   the   other   hand,   unless   we 


VISUAL  CONTRAST  .       15 

are  prepared  to  make  the  correction,  we  are  constantly 
deceived  as  to  the  strength  of  lights  and  shades.* 

2.  Color-contrast. — Lay  any  two  color-squares  upon 
the  background;  lay  one  of  the  gray  bars  upon  each  of 
the  colors  and  cover  with  the  tissue-paper.  Observe 
that  the  gray  of  each  bar  assumes  a  distinct  color-tinge. 
Kecord  the  color  of  each  bar.  Kepeat  the  same  with 
other  color-squares,  pair  by  pair.  If  possible  reduce 
these  records  to  a  law  of  color-contrast. t 

The  two  bars  are  colorless — exactly  the  same  gray, 
yet  each  shows  a  distinct  tinge  of  color.  Those  who  fail 
to  see  one  or  more  of  the  contrast-colors  of  these  figures 


*  Supplementary  Experiment. —  (Not  to  be  performed  unless 
directed  by  the  instructor.)  The  following  measurement  of 
brightness-contrast  is  very  simple  and  effective  and  may  be  dem- 
onstrated if  a  color-wheel  or  a  color-top  is  available.  Revolve 
a  black  and  a  white  disk  upon  the  color-wheel  and  adjust  the 
proportions  of  black  and  white  until  the  resulting  gray  matches 
the  gray  bar  on  one  square.  Record  the  amount  of  white  in  the 
mixture.  Then  measure  the  grayness  of  the  other  square  in 
the  same  manner.  The  difference  in  the  amount  of  white  in  the 
two  measurements  is  a  measure  of  the  difference  between  the 
two  gray  bars. 

By  similar  procedure  it  is  easy  to  determine  how  much  of  this 
contrast-effect  is  due  to  the  white  and  the  black  fields  re- 
spectively. 

f  A  very  pretty  demonstration  of  color-contrast  may  be  made 
as  follows:  Put  a  large  white  paper  or  cloth  upon  a  table;  place 
upon  it  some  tall,  slender  object  which  will  cast  a  long,  narrow 
shadow;  pull  down  all  window-shades  except  one  which  is  left 
open  about  a  foot;  light  a  candle  or  any  other  artificial  light 
and  hold  it  a  little  to  the  side  of  the  window.  There  will  be 
two  shadows  of  the  object,  one  from  the  white  daylight  and  the 
other  from  the  yellow  artificial  light.  The  latter  shadow  is  seen 
distinctly  blue.  In  reality,  or  physically,  it  is  gray;  the  blue 
is  the  contrast  from  the  surroundings  which  are  made  yellow 
by  the  artificial  light.  The  induced  blue  is  a  much  stronger  color 
than  the  inducing  yellow. 


16  VISUAL  CONTRAST 

after  a  fair  trial  have  a  corresponding  color-blindness  or 
color-weakness,  which  can  be  measured. 

Color-contrast  is  most  effective  when  there  is  no 
brightness-contrast  between  the  two  fields.  The  effect 
would  have  been  very  much  enhanced  in  the  present 
figures  if  each  gray  bar  had  been  matched  in  brightness 
with  the  color-field  upon  which  it  rested.  An  otherwise 
strong  color-contrast  may  be  almost  obliterated  by  the 
introduction  of  a  simultaneous  brightness-contrast.* 

Here  again  we  have  a  sweeping  principle:  all  colors 
tinge  their  surroundings  with  their  complementary 
color.  Things  are  not  what  they  seem !  The  colors  in 
nature,  art,  fabrics — everywhere — are  active  and  mod- 
ify their  environments.  Flowers  and  foliage,  grass  and 
sky,  all  play  their  harmonies  and  discords  in  modula- 
tions of  color.  The  artist  trusts  the  subjective  colors  as 
surely  as  he  trusts  the  pigment  on  his  canvas.  The  mil- 
liner and  the  modiste  use  contrast  effectively  and 
artistically:  a  dark  hat  and  a  green  gown  give  a  fair 
and  rosy  complexion.  There  is  almost  as  much  in  the 
art  of  knowing  what  to  avoid  as  in  knowing  what  to 
employ,  t 

3.  Brightness-effect  on  Color. — Lay  the  black  and 
the  white  squares  upon  the  background ;  lay  one  of  the 

*-The  color-contrast  may  be  measured  on  the  same  principle 
as  the  brightness-contrast. 

•]•  Chevreiil,  "The  Laws  of  Contrast  of  Color  and  their  Appli- 
cation to  the  Arts  of  Painting,  Decoration  of  Buildings,  Mosaic 
Work,  Tapestry  and  Carpet-weaving,  Calico-printing,  Dress, 
Paper-staining,  Printing,  Military  Clothing,  Illumination,  Land- 
scape-gardening, etc.,"  is  an  interesting  book,  though  somewhat 
out  of  date. 


VISUAL  CONTRAST  17 

green  bars  upon  each  of  these  and  cover  with  tissue- 
paper.  Record  the  effect  of  the  black  and  the  white 
upon  the  green. 

The  colorless  brightness  of  the  surroundings  modifies 
the  color  near  it.  When  placed  upon  similar  fields,  the 
two  greens  are  exactly  alike ;  but  when  placed  upon 
fields  which  differ  in  brightness,  the  greens  appear  to 
change  in  brightness  according  to  the  laws  of  brightness- 
contrast.  A  dark  field  makes  an  adjacent  color  brighter, 
a  light  field  makes  it  darker. 

4.  Color-effect  on  Color,  a.  Canceling. — Lay  the 
green  and  the  gray  squares  upon  the  white  background ; 
lay  a  pale  green  bar  upon  each  one  and  cover  with  the 
tissue-]3aper.  Record  the  effect  of  the  deep  green  upon 
the  pale  green. 

h.  Enhancing. — Lay  one  green  bar  upon  the  red 
square  and  the  other  upon  the  gray  and  cover  Avith  the 
tissue-iDaper.  Record  the  effect  of  the  red  upon  the 
green. 

c.  Modulating. — Lay  the  yellow  and  the  blue  squares 
upon  the  background ;  lay  a  green  bar  upon  each  one  and 
cover  w^ith  the  tissue-paper.  Record  the  apparent 
change  in  the  color-tone  of  the  two  bars. 

These  three  variations  represent  the  three  types  of 
effect  of  one  color  upon  another.  The  two  pale-green 
bars  are  alike,  but  the  one  upon  the  green  tends  to  lose 
its  color,  while  the  one  on  the  red  is  enhanced  in  color. 
The  green  square  throws  a  contrast  red  upon  its  bar  and 
this  tends  to  cancel  the  green  and  produce  a  gray.  This 
illustrates  how  one  color  tends  to  obliterate  a  neighbor- 


18  VISUAL  CONTRAST 

ing  color.  Wherever  shades  or  tints  run  together  with 
a  more  saturated  form  of  the  same  color,  the  weaker 
color  must  be  made  stronger  to  compensate  for  the  loss 
by  contrast  with  its  own  but  stronger  color. 

The  field  of  the  red  square  induces  a  contrast  green 
which  reinforces  the  original  green  of  the  bar.  The 
effect  of  the  red  upon  the  green  illustrates  the  general 
law  that  opposites  enhance  each  other,  which  is  true  for 
both  brightness  and  color. 

The  green  on  the  yellow  field  looks  bluish  green 
and  the  one  on  the  blue  field  looks  yellowish  green. 
These  are  illustrations  of  the  law  that  colors  which 
are  not  complementary  or  identical  have  a  modulat- 
ing effect  upon  each  other.  This  is  by  far  the  most 
frequent  of  the  three  types  of  the  effect  of  color  upon 
color. 

This  condition,  that  every  color  changes  adjoining 
colors,  reduces  itself,  then,  to  a  simple  order  and  an 
easily  applicable  law.  The  effect  can  always  be  pre- 
dicted. Knowing  the  series  of  complementaries  and  the 
principles  of  color-mixing,  we  can  always  predict  the 
result. 

All  these  contrast-phenomena  are  very  much  stronger 
in  ordinary  experience  than  under  these  experimental 
conditions,  because,  in  the  experiment,  we  are  not  only 
in  a  more  critical  attitude,  but  we  are  also  biased  by 
the  knowledge  of  the  actual  conditions,  e.g.,  that 
the  gray  bars  are  alike  and  that  the  green  bars 
are  alike.  In  nature  and  in  art,  especially  where  we 
are  not  conscious  of  the  contrast,  the  illusion  has  full 
play. 


VISUAL  CONTRAST  19 

5.  Effect  Immediate,  a.  Direct  Observation. — Ke- 
peat  Exps.  1  and  2  and  observe  that  the  contrast  is  pres- 
ent as  soon  as  the  object  is  clearly  seen. 

h.  Comparison  with  After-images. — Determine  the 
shortest  exposure-time  which  will  bring  out  a  noticeable 
after-image  of  the  black  square.  Kecord  the  approx- 
imate time. 

This  experiment  proves  two  things:  first,  that  the 
purely  simultaneous  contrast-effect  is  immediate  and 
is  not  due  to  adaptation;  and,  second,  that  it  is  very 
closely  related  to  the  adaptation  of  successive  contrast 
or  after-images  in  effect,  so  that  the  greatest  care  must 
be  taken  to  avoid  complication  of  the  two  kinds  of  con- 
trast as  far  as  possible.  After  some  training  in  obser- 
vation one  may  obtain  an  after-image  from  a  mere 
glance  at  the  figure.  We  seldom  see  an  object  so  quickly 
that  adaptation  does  not  play  a  role  in  the  perception. 

6.  Effect  Marginal  and  Reciprocal. — Lay  the  green, 
the  yellowish-green,  the  greenish-yellow,  and  the  yellow 
color-squares  side  by  side  in  the  order  named,  with  edges 
slightly  overlapping.  Observe  them  both  with  and 
without  the  tissue-paper  cover.  Describe  the  changes  in 
these  colors  which  are  due  to  the  juxtaposition. 

Contrast,  whether  of  brightness  or  color,  is  always 
reciprocal.  Which  of  the  two  or  more  fields  shall  show 
the  greatest  effect  depends  upon  the  means  of  compari- 
son, the  relative  area,  the  relative  brightness,  the 
relative  saturation,  the  j)oint  of  regard,  and  many  other 
conditions.  When  seen  by  itself,  each  of  these  squares 
is  of  uniform  color  and  brightness;  but  when  seen  to- 


20  VISUAL  CONTRAST 

getlier,  the  green  brings  out  the  yellow  of  the  adjoining 
less  green  square  by  counterbalancing  the  green  of  the 
contrast  red.  The  yellow  brings  out  the  green  of  the 
less  yellow  square  by  counterbalancing  the  yellow  with 
the  contrast  blue.  Each  color  makes  the  different  ele- 
ment in  the  contiguous  color  more  conspicuous.  Tlie 
effect  is  striking  even  without  the  elimination  of  con- 
tour by  the  tissue-paper.  When  the  effect  tapers  off 
rapidly  from  the  margin,  as  in  this  case,  it  is  spoken 
of  as  marginal  contrast. 

Marginal  contrast  is  one  aspect  of  the  general  prin- 
ciple that  the  contrast-effect  decreases  with  increase  in 
the  distance  between  the  two  contrasting  surfaces. 
Certain  conditions  tend  to  make  it  prominent,  as  here, 
but  there  has  been  opportunity  for  observing  the  fact 
in  every  experiment. 

7.  Area. — Place  a  gray  bar  and  the  gray  square  some 
distance  apart  upon  the  background  and  cover  with  the 
tissue-paper.    Record  which  appears  to  be  the  darker. 

The  two  gi'ays  are  really  alike,  but  the  bar  looks  the 
darker  on  account  of  its  relatively  small  area  and  the 
form  which  is  favorable  to  the  exposure  from  the  white 
inducing  field.  In  all  the  above  experiments  the  effects 
have  been  reciprocal,  but  we  have  directed  our  attention 
to  the  smaller  areas  because  they  show  the  greatest 
relative  effect. 

8.  Contour. — Compare  the  force  of  the  contrast  in 
Exps.  1  and  2  when  the  squares  are  covered  with  the  tis- 
sue-paper witli  the  force  when  they  are  not  covered. 
Record  the  difference  in  the  effect. 


VISUAL  CONTRAST  21 

The  observer  has  imdoubtedly  been  annoyed  and 
puzzled  by  the  constant  demand  for  covering  with 
tissue-paper.  What  can  be  its  jDurpose  ?  The  tissue- 
paper  has  been  employed  for  the  purpose  of  eliminating 
contour,  and  that  only.  This  has  been  done  on  the 
principle  that  contrast  is  very  much  enhanced  by  un- 
certainty in  the  surface.  Surfaces  with  very  sharp 
delineations  counteract  the  motives  for  contrast. 

There  are  other  ways  of  eliminating  contour.  'Nsl- 
ture  as  a  rule  presents  more  or  less  uncertain  contour 
and  therefore  favors  contrast.  Distance,  for  example, 
serves  the  same  purpose  as  the  tissue-paper.  When  we 
admire  a  flower-bed  or  a  landscape  we  are  far  enough 
away  to  get  the  dim  outline  and  the  vagueness  of  con- 
tour which  are  so  favorable  for  contrast.* 

9.  Contrast  in  the  After-image. — Lay  one  gray  bar 
upon  the  black  square  and  the  other  near  by  upon  the 
white  background ;  cover  with  tissue-paper.  Fixate  a 
point  between  them  and  secure  an  after-image.  Record 
the  relative  brightness  of  the  two  bars  in  the  after- 
image. 

The  contrast  is  effective  in  the  after-image. 

The  explanation  of  visual  contrast  in  color  and 
brightness  is  probably  to  be  found  chiefly  in  physiologi- 
cal terms^ — in  the  indirect  stimulation  of  adjacent  areas 
of  the  retina. 


*  The  color-wheel  serves  the  same  purpose.  If  we  cut  three 
concentric  gray  circles  of  different  brightness  and  place  them  on 
the  wheel,  the  contrast  will  hardly  be  perceptible  so  long  as  the 
wheel  is  motionless;  but  revolve  the  disk  and  the  contrast  at  once 
becomes  conspicuous,  because  the  spinning  takes  away  the  sharp 
rigidity  of  outline  and  surface. 


22  VISUAL  CONTRAST 

The  experiments  have  all  been  devoted  to  color  and 
brightness.  The  phenomena  of  visual  contrast  might 
have  been  equally  well  illustrated  in  visual  perception 
of  space.  The  general  law  is  that  opposites  enhance 
each  other  although  the  actual  explanation  for  this  may 
be  different  in  different  cases.  As  black  enhances  white 
and  red  enhances  green,  so  there  is  a  reciprocal  enhance- 
ment betAveen  the  long  and  the  short,  the  large  and  the 
small,  the  narrow  and  the  wide,  the  irregular  and  the 
regular,  the  dull  and  the  sharp,  the  smooth  and 
the  rough,  the  straight  and  the  crooked,  the  ugly  and 
the  beautiful,  etc.  When  the  tall  and  the  short  man 
walk  together,  the  tall  one  looks  taller  and  the  short 
one  looks  shorter  than  otherwise.  A  poor  penman  is 
mortified  to  see  his  signature  together  with  the  signa- 
ture of  a  good  penman.  A  pocket-knife  is  dull  in  com- 
parison with  a  razor,  but  sharp  in  comparison  with  a 
hatchet. 

Similar  illustrations  might  be  found  in  the  time,  or 
duration,  of  visual  acts.  Contrast  operates  in  all  the 
attributes  of  sensation — quality,  intensity,  duration, 
and  space.  And  we  find  it  in  all  the  senses.  Indeed, 
one  of  the  laws  of  contrast  is  that  it  is  strongest  in 
those  senses  with  which  we  make  the  poorest  discrimina- 
tion. Hence  the  most  striking  illustrations  of  contrast 
are  found  in  the  lower  senses,  as  in  taste,  smell,  and 
temperature. 


CHAPTER  III 
THE  VISUAL  FIELD 

For  One. 

Tjie  problem  is  to  measure  the  field  of  vision  for 
white  and  colors,  and  to  determine  some  characteristic 
color-changes  in  the  indirect  field. 

Make  the  following  preparation  for  the  experiment: 
Lay  a  piece  of  cardboard  back  of  Fig.  1.  Prick  through 
the  page  with  a  pin  at  each  nmnber  on  the  arc,  at  the 
free  end  of  the  heavy  line,  and  at  the  principal  points  in 
the  light  line.  Trim  the  card  by  cutting  according  to 
the  tracing  of  the  light  line.  Insert  the  degree-numbers 
at  the  appropriate  points.  Draw  the  heavy  line. 
Punch  a  pinhole  at  the  free  end  of  the  heavy  line, 
which  is  the  center  of  the  arc.  Put  a  thread  through 
the  hole  and  tie  a  knot  at  the  back  of  the  card.  Tie  a 
knot  at  the  other  end  of  the  thread,  fifty  centimeters 
away.  Take  the  large  black  square  and  the  small  white, 
red,  green,  yellow,  and  blue  squares  from  the  book  envel- 
ope. Lay  the  white  square  upon  the  large  black  square 
as  a  background;  then  stick  a  pin  through  the  knot  at 
the  free  end  of  the  cord,  through  the  two  squares  near 
a  corner  of  the  small  one,  and  finally  through  a  cork 

23 


24 


THE  VISUAL  FIELD 


which  may  serve  as  a  handle.     The  quadrant  and  ob- 
ject-card thus  arranged  may  be  called  a  perimeter.* 


Fig.  1. 

The  perimeter  is  a  simple  means  of  measuring  the 
direction  of  an  object  in  the  indirect  field  of  vision. 

*  There  have  been  two  general  types  of  instruments  employed 
in  perimetry  of  vision :  { 1 )  those  in  which  the  measurements 
are  made  upon  a  plane  surface,  and  (2)  those  in  which  the 
measurements  are  made  upon  the  arc  of  a  circle  centered  at 
the  eye.  The  former  is  called  a  campimeter,  the  latter  a  per- 
imeter. The  present  outfit  works  on  the  perimeter  principle. 
The  most  effective  perimeter  is  an  instrument  with  colored  lights 
in  a  daric  room. 


THE  VISUAL  FIELD  25 

Seat  yourself  in  good  reflected  light  with  the  back 
toward  the  source  of  light.  Mark  a  dot  on  a  piece  of 
white  paper  and  fasten  it  up  sixty  centimeters  directly 
in  front  of  the  eyes.  Blindfold  one  eye ;  hold  the 
quadrant  with  one  edge  close  to  the  other  eye  so  that 
in  looking  straight  forward  at  the  dot,  the  eye  sights 
along  the  heavy  straight  line  on  the  quadrant.  When 
the  eye  is  fixed  upon  it,  the  dot  becomes  the  fixation- 
point,  or  point  of  regard,  and  is  said  to  lie  in  the  direct 
field  of  vision.  The  visual  space  around  it  is  spoken  of 
as  the  indirect  field. 

1.  The  Field  for  White.— Hold  the  quadrant  in 
the  horizontal  plane  in  front  of  the  right  eye  so  that 
the  regard-line  on  the  quadrant  points  exactly  toward 
the  fixation-point  when  you  sight  along  it.  Keep  the 
head  upright  and  firm.  Fixate  the  dot  which  is  the 
point  of  regard  and  do  not  allow  the  eye  to  wander  away 
from  it  during  the  actual  trial.  Move  the  object-card 
inward  from  the  extreme  right  until  the  white  disk  can 
first  be  seen  as  white.*  The  thread  being  held  taut 
will  indicate  the  number  of  degrees  from  the  line  of 
regard.  Record  this.  Make  five  trials,  and  find  the 
average  and  the  mean  variation  for  these.f 

Proceed  in  the  same  manner  and  measure  along  the 
other  three  cardinal  radii,  namely,  with  the  white  enter- 
ing from  below,  from  the  left,  and  from  above. 

*  Move  inward  at  such  a  rate  that  the  destination  is  reached 
in  about  eight  seconds.  Take  special  care  that  the  head  does 
not  turn  or  the  eye  wander  from  the  point  of  regard,  and  that 
the  point  of  regard  is  directly  in  front  of  the  eye. 

f  The  mean  variation  (m.  v. )  is  a  measure  of  the  degree  of 
agreement  in  a  series  of  records.     It  represents   the  average  of 


26  THE  VISUAL  FIELD 

To  represent  these  results  graphically,  draw  four 
radii  from  a  point  representing  the  point  of  regard — 
one  to  the  right,  one  to  the  left,  one  down,  and  one 
up, — and  place  a  dot  on  each  radius  to  represent  the 
corresponding  measurement  on  the  scale  of  one  milli- 
meter to  one  degree.     Mark  each  of  these  dots  w."^ 

These  results  are  stated  with  reference  to  the  field 
of  vision ;  they  might  equally  well  have  been  stated  in 
terms  of  regions  on  the  retina.  The  outer  or  temporal 
field  of  vision  corresponds  to  the  inner  or  nasal  region 
of  the  retina,  and  the  upper  field  of  vision  corresponds 
to  the  lower  region  of  the  retina.  The  temporal  field 
of  vision  is  larger  than  the  nasal,  and  the  lower  is 
larger  than  the  upper.  This  difference  is  due  to  the 
limitations  placed  by  the  nose,  cheek-bone,  and 
brow.t 


the  deviations  of  each  individual  record  from  the  average  of  all 
the  records  for  the  group,  regardless  of  sign.     Thus 


75    - 

1 

73    - 

3 

78    - 

2 

80    - 

4 

75    - 

1 

5)381  5)11 

Ave.  76         2.2  m.  V. 

*Thus,  if  the  white  square  was  first  seen  as  white  at  fifty  de- 
grees above  the  eye,  put  a  dot  fifty  millimeters  from  the  center 
on  the  appropriate  radius. 

f  Supplementary  Exercise. — There  is  a  totally  blind  spot  in  the 
nasal  region  of  each  eye.  It  is  located  at  the  point  of  entrance 
of  the  optic  nerve,  about  fifteen  degrees  from  the  fovea,  or  point 
of  clearest  vision.  If  this  exercise  is  assigned,  the  student  should 
devise  his  own  methods  and  means  for  one  or  more  of  three 
exercises:  (1)  to  locate  the  blind  spot;  (2)  to  survey  and  de- 
termine its  shape  and  area;  and  (3)  to  determine  how  it  is  filled 
out  in  perception. 


THE  VISUAL  FIELD  27 

2.  The  Fields  for  Colors. — Substitute  the  red  square 
for  the  white  and  determine  the  limits  ^  for  red  on  the 
two  meridians,  right  and  down,  making  five  trials  for 
each.t  Compute  the  average  and  mean  variation  and 
insert  the  averages  on  the  two  corresponding  radii  of  the 
chart  for  Exp.  1  and  mark  them  r. 

Measure  and  record  in  the  same  manner  for  yellow, 
blue,  and  green. 

Assuming  that  the  results  for  the  meridians  selected 
are  typical  of  what  we  should  find  in  the  other  me- 
ridians in  regard  to  the  order  of  limits,  this  and  the 
foregoing  experiments  demonstrate  that  the  color-fields 
are  all  smaller  than  the  field  for  white;  and,  in  the 
normal  eye,  the  colors  supplied  have  fields  which  vary 
in  magnitude  in  the  order  yellow,  blue,  red,  and  green. 
There  is  such  a  large  difference  that  the  field  for  green 
has  less  than  one-fourth  the  area  of  the  field  for  yellow. 

How  does  this  affect  our  ordinary  perception  of 
color  in  the  indirect  field  of  vision?  If  we  look 
steadily  at  one  flower  in  a  flower-bed  and  attempt, 
without  movement  of  the  eyes,  to  see  the  coloration  of 
the  whole  bed,  we  observe  that,  outside  of  a  certain 
narrow  limit,  the  leaves  do  not  look  green;  beyond  a 
somewhat  larger  limit,  no  flowers  are  seen  red,  al- 
though the  blue  and  yellow  ones  look  brilliant;  and  in 
the  outermost  parts  of  the  bed  all  flowers  and  leaves 

*  The  observer  knows  what  the  color  is  to  be,  and  the  task 
is  to  discover  the  limit  at  which  he  can  identify  the  disk  as  be- 
ing of  that  particular  color.  The  inward  movement  should  begin 
just  clearly  outside  the  field  and  be  made  at  such  a  rate  that 
the  limit  is  reached  in  from  five  to  ten  seconds. 

f  If  desired,  these  color  squares  may  be  cut  smaller,  but  the  size 
must  be  recorded. 


28  THE  VISUAL  FIELD 

look  gray.  This  is  literally  true,  but  not  alarming, 
because  we  do  not  usually  look  at  flower-beds  in  that 
way.  When  we  Avant  to  see  the  color  of  a  bed  of  flow- 
ers, a  painting,  or  a  sky,  we  regard  (that  is,  pay  at- 
tention to),  or  apperceive,  only  the  color  of  the  direct 
field  at  and  around  the  point  of  regard ;  our  eyes  sweep 
back  and  forth  over  the  object  automatically  with  as- 
tonishing swiftness  and  take  a  series  of  snaj^shots,  as 
it  were,  on  the  central  portion  of  the  retina,  and  then 
we  combine  these  into  a  whole  in  memory,  although  the 
process  is  almost  instantaneous  and  seems  to  be  a  single 
act  of  perception.  We  have  the  feeling  that  the  color- 
impressions  from  the  direct  and  indirect  fields  are 
simultaneous,  but  the  fact  is  that  we  have  memory- 
images  of  impressions  from  different  parts  of  the  object 
and  the  simultaneous  impressions  from  the  whole  object 
become  merely  a  sort  of  plat  on  which  we  unconsciously 
distribute  these  impressions  and  reconstruct  the  true 
color-relations. 

If  we  had  used  the  four  truly  fundamental  colors,* 
the  absolutely  complementary  pairs,  yellow  and  blue, 
and  red  and  bluish  green,  and  had  reduced  them  to  the 
same  brightness  and  saturation,  we  should  have  found 
that  the  limits  for  blue  and  yellow  coincide  and  those 
for  red  and  gTeen  coincide.  In  Fig.  2  the  inner  curve 
represents  the  red-green  boundary  and  the  outer  the 
yellow-blue  boundary.     The  shading  shows  the  limit  for 


*  The  colors  which  answer  for  this  purpose  are  very  difficult  to 
obtain.  Tliose  furnished  are  neither  fully  complementary  nor  of 
the  right  hue  as  fundamental  colors.  They  also  differ  much  iu 
brightness. 


THE  VISUAL  FIELD 


29 


white    and    slioiild    be    compared    with    the    record    in 
Exp.  1. 

Thns,  the  retina  may  be  conceived  of  as  being  divided 
into  three  zones:  (1)  a  central  zone  over  which  all 
colors  and  brightnesses  can  be  seen;  (2)  a  middle  zone 
over  which  only  bines  and  yellows  and  their  derivatives 
can  be  seen;  and  (3)  an  outermost  zone  over  which  all 
objects,  colored  and  nncolored,  appear  gray.     Let  ns 


Fig.  2. 
note  some  of  the  most  significant  applications  of  this  law 
of  distribution. 

Color-vision  is  made  possible  by  the  existence  in  the 
retina  of  the  so-called  color-elements.  There  are  many 
theories  in  regard  to  the  probable  number  of  these. 
The  close  coincidence  of  these  two  pairs  of  colors  tends 
to  support  the  conjecture  that  the  retina  contains  either 


30  THE  VISUAL  FIELD 

two  doubly-functioning  or  two  pairs  of  color-elements, 
one  for  red-green  and  one  for  yellow-blue.  The  psycho- 
logical chart  of  the  fields  of  color-vision  must  therefore 
be  used  as  one  of  the  criteria  of  a  physiological  theory 
of  the  nature  and  distribution  of  the  color-elements. 

The  three  zones  probably  indicate  as  many  epochs  in 
the  evolution  of  color-vision.  The  primitive  eye  was 
sensitive  only  to  brightness ;  some  of  these  elements  in 
the  central  portion  of  the  retina  differentiated  and  be- 
came sensitive  to  yellow  and  blue,  and  these  elements 
spread  gradually,  during  evolutionary  ages,  from  the 
fovea  to  the  periphery  of  the  retina  and  have  now 
reached  the  expanse  outlined  by  the  yellow-blue  curve 
in  the  chart ;  very  much  later,  a  higher  differentiation 
of  the  elements  at  the  fovea  resulted  in  the  development 
of  sensitiveness  to  red  and  green  and  these  elements 
are  now  spreading  toward  the  periphery  but  have  not 
yet  reached  farther  than  the  limits  which  correspond 
to  the  red-green  curve  in  Fig.  2.* 

This  arrangement  also  becomes  an  explanation  for 
the  well-known  fact  about  color-blindness,  that  by  far 
the  most  numerous  cases  of  color-blindness  are  of  the 
red-green  type.  Why  should  this  be  so  ?  There  is  a 
well-kno^\Ti  biological  law  to  the  effect  that,  in  general, 
the  last  acquired  structure  is  the  first  to  become  defec- 
tive or  to  be  lost.  ^N'ow,  the  red-green  elements  are  the 
least  stable  because  they  have  been  acquired  most 
recently,  and  therefore  a  person  is  much  more  likely 


*  All  colors  other  than  the  fundamental  are  mixtures  of  two 
or  more  of  the  fundamental  colors.  Hence  the  four  color-elements 
can  produce  all  the  experienced  color-effects. 


THE  VISUAL  FIELD  31 

to  be  red-green  blind  than  yellow-blue  blind,  if  his  color- 
vision  is  defective. 

These  zones,  as  determined  in  the  experiments  upon 
which  Fig.  2  is  based,  are  not  fixed  except  for  the  par- 
ticular conditions  specified.  Among  the  conditions 
which  determine  the  limits  of  the  zones  the  following 
may  be  noted : 

a.  Color  tone. — The  four  colors  in  this  experiment 
go  by  the  same  name  as  the  four  upon  which  Fig.  2 
is  based,  but  the  two  sets  of  colors  differ  very  much  in 
tone  and  the  results  vary  accordingly. 

h.  Saturation  or  Purity. —  As  a  rule,  the  purer  the 
color  the  larger  the  field. 

c.  Btnghtness. — The  brighter  the  color  or  the  gray 
the  larger  will  be  its  field.  One  of  the  chief  causes  for 
the  difference  between  the  record  in  this  experiment  and 
in  the  curves  in  Fig.  2  is  that  of  brightness ;  in  a  stand- 
ard experiment  the  colors  are  all  reduced  to  the  same 
brightness,  while  in  the  common  tones  as  here  used 
there  is  a  great  difference  in  brightness.  As  the  illu- 
mination of  the  colored  stimulus  is  increased  the  field 
is  enlarged. 

d.  Area  or  Magnitude. — Within  certain  limits,  the 
larger  the  colored  object  the  larger  is  its  field. 

e.  Background. — The  background  has  profound  in- 
fluence upon  the  color.  Numerous  laws  of  the  rela- 
tion of  the  peripheral  color  to  its  background  have  been 
worked  out.  In  general  for  mixed  colors  (all  pigment 
colors)  the  field  is  largest  when  the  contrast  between 
the  background  and  the  color  is  the  greatest. 

/.  Adaptation  and  Fatigue. — It  makes  a  difference 


32  THE  VISUAL  FIELD 

whether  the  eye  has  become  adapted  to  darkness  or  to 
some  kind  of  light  before  a  trial.  The  rested  eye  is 
more  efficient  and  gives  a  larger  field  than  the  non- 
rested  eye.  Retinal  fatigue  shows  itself  more  rapidly 
in  a  retinal  area  the  farther  the  area  is  away  from  the 
fovea.  We  have  only  to  recall  what  we  learned  in  the 
two  foregoing  chapters  to  realize  what  a  large  variable 
this  is.  It  is  necessary  to  make  comparatively  rapid 
movements  in  order  to  secure  the  best  results. 

g.  Practice. — It  is  probable  that  the  extension  of  the 
color-fields  as  the  result  of  practice  is  not  an  increase 
of  sensitivity  in  the  retinal  elements,  but  merely  a  de- 
velopment in  capacity  for  observation. 

li.  Age. — Color-fields  enlarge  with  age.  The  differ- 
ence between  the  field  of  a  boy  of  ten  years  and  one 
of  twenty  is  large;  but  we  do  not  know  how  much  of 
this  is  due  merely  to  the  former's  lack  of  power  in  appli- 
cation and  skill  in  observation. 

i.  Disease. — Certain  nervous  diseases  are  character- 
ized by  peculiar  changes  in  the  fields  of  color.  There 
may  be,  for  example,  general  contraction  of  the  color- 
fields,  loss  of  vision  in  one  half  of  the  retina,  impair- 
ment in  the  vision  of  certain  colors,  or  central  color- 
blindness. This  last-named  defect  often  results  from 
nicotine-poisoning;  it  is  discovered  by  the  fact  that,  in 
order  to  see  colors,  the  patient  must  view  the  object  by 
indirect  vision. 

j.  Color-hlindness. — This  is  a  large  topic  by  itself. 
About  one  per  cent  of  all  women  and  more  than  four 
per  cent  of  all  men  are  distinctly  blind  to  some  colors ; 
and  indeed  the  most  recent  and  most  efficient  tests  of 


THE  VISUAL  FIELD  33 

color-blindness  make  it  seem  probable  that  these  figures 
are  underestimations.  'No  one  can  have  come  success- 
fully to  the  present  stage  in  this  course  without  dis- 
covering whether  or  not  his  color-vision  is  defective. 

Jc.  Arbitrary  Limits. — A  color  comes  into  its  field 
gradually ;  the  magnitude  of  the  field  therefore  depends 
upon  what  degree  of  resemblance  to  the  color  as  seen 
in  direct  vision  the  observer  has  set  himself  as  a 
standard  for  the  purpose  of  the  measurement.  The 
incoming  color  is  never  exactly  like  the  color  as  known 
through  direct  vision. 

3.  Transition  Colors. — Starting  to  the  right,  outside 
the  color-field,  and  going  by  ten-degree  steps  toward  the 
point  of  regard,  observe  and  record  the  color  of  the  red 
square  as  it  appears  at  the  first  momentary  impression 
in  each  step.    Make  three  independent  series  of  trials."^ 

Eecord  three  series  of  observations  for  yellow  in  the 
same  manner. t 

According  to  the  Hering  theory  of  color-vision,  there 
are  four  '^Urfarben",  that  is,  primary  or  fundamental 
colors.  All  other  colors  may  be  built  up  from  these, 
and  to  them  the  color  elements  in  the  retina  correspond. 
They  are  the  two  pairs  of  perfect  complementaries 
spoken  of  in  Exp.  2.  They  undergo  no  change  when 
passed  outward  through  the  indirect  field  and  are  there- 
fore  called   stable   colors.      All   other   than   the   stable 

*  If  the  right  eye  shows  fatigue,  this  and  the  following  ex- 
periments may  be  made  with  the  left  eye.  The  practice  gained, 
however,  makes  it  easier  to  use  the  right  eye. 

■j-  The  record  must  necessarily  be  a  crude  description  of  the 
changes  in  color  and  brightness. 


84  THE  VISUAL  FIELD 

colors  undergo  more  or  less  radical  changes  when  passed 
through  the  indirect  field,  as  in  this  experiment.  The 
following  is  a  typical  record,  though  much  abbreviated:* 


^,  •  Transition  colot'S :  the  same  color  wJien 

i,oior  as  seen  m  passed   inivard    thrcnigh    the  indirect 

lite  direct  jieia.  fi^i^  appeared  successively  as  follows. • 

Deep  red  Yellowish,  yellow,  orangisli  yellow,  yellow- 
orange,  orange-red,  red. 

Reddish  orange    Yellowish,  orangish  yellow,  reddish  orange. 

Orange-yellow     Yellowish,  yellow,  orangish  yellow. 

Green     Yellowish,  yellow,  greenish  yellow,  green. 

Blue   Blue.    (This  happened  to  be  the  stable  blue.) 

Violet     Bluish,  blue,  violet. 

Purple  (red  end)  ...Yellowish,  orange-yelloAV,  yellow-orange, 
orange-red,  red,  purplish  red,  reddish  pur- 
ple, purple. 


This  record  expresses  a  general  law:  the  colors  of 
the  red  end  of  the  spectrum  first  appear  as  yellowish  or 
yellow  in  the  outer  regions  of  the  field  of  vision,  while 
those  of  the  blue  end  first  appear  as  bluish  or  blue. 
Red,  orange,  yellow,  and  green  come  in  with  a  yellow- 
ish tinge,  while  blue  and  violet  come  in  with  a  bluish  or 
blue  tinge. 

Every  color  enters  the  field  of  vision  as  a  gray. 
Within  the  yellow-blue  zone  all  colors  appear  in  some 
aspect  of  yellow  or  blue,  if  they  are  seen  as  colors. 
Only  within  the  central  zone  can  the  reds  and  greens 
and  their  derivatives  reveal  their  true  color.  A  com- 
parison of  this  statement  with  the  above  law  makes 
what  is  otherwise  an  apparently  chaotic  condition  of 
affairs  seem  natural  and  intelligible. 


'to-" 


*From  Baird's  "The  Color-sensitivity  of  the  Peripheral  Retina," 
Publication  29,  Carnegie  Institution.  The  present  chapter  is  based 
mainly  upon  this  monograph. 


i 


THE  VISUAL  FIELD  35 

The  pigment  colors  of  papers  and  fabrics  are  always 
mixed  colors.  The  reds,  oranges,  and  greens,  for  ex- 
ample, contain  considerable  yellow,  and  it  is  this  yellow 
which  becomes  dominant  and  represents  those  colors 
within  the  yellow-blue  zone.  In  the  same  way,  it  is  the 
blue  of  the  violet  end  which  represents  violet  outside 
of  the  red  zone. 

All  colors  also  undergo  characteristic  changes  in 
brightness  in  passing  through  the  indirect  field. 

4.  Adaptation  Colors. — Hold  the  red  square  at  25° 
on  the  right  meridian  for  about  ten  seconds,  being  care- 
ful to  maintain  a  steady  fixation  on  the  point  of  regard, 
and  observe  the  changes  the  color  goes  through  in  that 
time.  Record  from  memory.  Make  three  trials,  allow- 
ing adequate  rest. 

Repeat  the  same  for  yellow. 

Constant  stimulation  of  a  given  area  of  the  peripheral 
retina  produces  definite  cycles  of  change  in  brightness 
and  color.  The  following  is  a  typical  record  of  the 
changes  for  three  seconds  by  a  trained  observer : 

,  Adaptation  colors  :    the  mccession 

Color  as  ^^^^ij^  of  colors  this  object  revealed  in  a 

the  direct  jield.  three-second  exposure  at  30°  right. 

Red    Red,  orange,  yellow,  white,  blue. 

Orange    Rich  orange,  yellowish  orange,  yellow. 

Yellow     Orange-yellow,  yellow,   gray,  bluish. 

Green    Yellow-green,  yellow,  gray,  bluish.      (25°.) 

Blue     Blue,  gray,  yellowish. 

Violet    Blue  ?,  blue,  bluish. 

Purple     Red,  orange-red,  orangish.      (25°.) 

From  records  of  this  kind  we  derive  a  law  which 
expresses  a  cycle  of  three  stages:  the  colors  of  the  red 


36  THE  VISUAL  FIELD 

end  of  the  spectrum  pass  toward  yellow,  and  those  of 
the  violet  end  toward  blue;  then  follows  a  momentary 
gray ;  and  then  appears  the  complementary  color  of  the 
one  jnst  before  the  gray. 

In  the  above  fragment  of  a  record,  these  three  stages 
are  represented  in  the  case  of  red,  yellow,  green,  and 
blue;  the  other  colors  did  not  complete  their  cycles 
within  the  time  limit. 

The  reasons  for  this  law  of  adaptation  are  as  fol- 
lows :  *     The  peripheral  retina  is  not  much  used  and 

*  Dr.  Baird  describes  this  process  in  a  personal  letter  as  fol- 
lows: "The  reasons  for  the  existence  of  these  characteristic 
phenomena  of  adaptation  or  exhaustion  are  these :  The  peripheral 
regions  of  the  retina  contain  but  a  relatively  scant  supply  of 
color-sensing  substance;  and  they,  too,  are  very  seldom  employed 
in  the  vision  of  every-day  life.  Consequently  the  advent  of 
retinal  exhaustion  must  be  relatively  rapid  when  these  regions 
are  stimulated.  Now,  the  pigment  colors  which  w^e  ordinarily 
see  are  not  pure,  but  mixed  colors;  green  leaves  and  red  ribbons 
contain  a  considerable  admixture  of  yellow,  orange,  blue,  etc. 
Hence,  when  a  colored  object  stimulates  the  peripheral  retina, 
its  stimulation  is  not  confined  to  a  single  color-sensing  substance, 
as  would  be  the  case  if  certain  pure  colors  were  employed.  The 
impure  red  of  the  ribbon  may  affect  both  the  red-sensing  sub- 
stance and  the  yellow-sensing  substance  of  the  retina.  Reasons 
for  believing  that  the  yellow-sensing  substance  is  more  stable  and 
persistent  in  function  than  the  red-sensing  substance  have  al- 
ready been  cited.  So  long  as  both  these  substances  continue 
to  function  in  approximately  equal  degree,  a  red  (or  yellowish 
red)  ribbon  will  be  seen.  But  in  proportion  as  the  red-sensing 
substance  becomes  exhausted — by  reason  of  its  scantiness  or  as 
a  result  of  its  lesser  tenacity  of  function — the  function  of  the 
yellow-sensing  substance  becomes  dominant  in  the  visual  process; 
the  ribbon  which  originally  seemed  red  now  appears  yellowish  or 
even  yellow.  This  marks  the  completion  of  the  first  phase  of 
the  color  process  of  indirect  vision,  and  the  beginning  of  the 
second  phase.  If  the  ribbon  still  continues  to  stimulate  the 
same  retinal  region,  the  yellow-sensing  substance  will  in  turn 
become  exhausted;  and  tlie  ribbon  will  appear  gray  so  long  as 
the  black- white  substance  continues  to  function  alone.  When 
this  third  stage  of  adaptation  is  reached  the  retinal  region  is 
completely    exhausted.      But    this   peculiar    condition   of    adapta- 


THE  VISUAL  FIELD  si 

therefore  fatigues  with  embarrassing  rapidity.  The 
colors  we  ordinarily  see  are  all  mixed,  and  the  yellow 
or  blue  element  in  a  mixture  is  more  stable  than  the 
red  or  green,  for  reasons  explained  under  Exp.  2  ;  hence 
the  latter  fatigues  more  quickly  and  falls  out,  leaving 
the  other  dominant.  This  is  the  goal  of  the  first  stage. 
Then  follows  the  process  of  adaptation,  as  in  after- 
images, when  the  stable  color  element  becomes  fatigued, 
and  leaves  a  blank  or  gray.  Then  follows  the  last  stage, 
which  corresponds  to  the  after-image  of  the  strongest 
element  in  the  first  stage. "^ 

The  fact  of  order  in  these  changes  is  perhaps  as 
astonishing  as  their  rapidity.  Our  common  experience 
of  these  changes  in  daily  life  has  resulted  simply  in  a 
distrust — both  conscious  and  unconscious — of  indirect 
color-vision.  When  we  think  of  it,  we  think  of  it  as 
chaotic;  when  we  inadvertently  follow  it,  we  feel 
uneasy;  in  normal  perception  we  automatically  neg- 
lect it. 

These  four  experiments  may  suffice  to  give  a  glimpse 
of  the  complexity  and  wonderful  arrangement  of  the 
color-fields  and  to  point  the  way  in  which  the  scientific 
attitude  is  rewarded  by  revelation  of  system  and  reason 


Hon  does  not  last  long.  A  process  of  regeneration  takes  place 
within  the  organ;  and  so  long  as  the  retinal  regeneration  contin- 
ues, one  sees  color  whether  the  colored  object  be  present  or  not. 
This  fonrth  stage  of  the  visual  process  is  analogous  to  that 
which  you  studied  in  your  experiments  with  after-images.  The 
visual  sensation  Avhich  now  appears  in  indirect  vision  is  com- 
plementary to  the  color  which  was  present  in  the  second  stage." 
*  It  is  remarkable  that  after-images  are  never  observed  in  the 
periphery  of  the  dark-adapted  retina,  and  very  rarely  more  than 
30°  from  the  fovea.  They  may  be  observed,  however,  in  the  per- 
iphery of  the  light-adapted  retina. 


38  THE  VISUAL  FIELD 

in  it  all.  Many  of  the  i)roblems  of  indirect  color-vision 
have  not  even  been  mentioned,  and  conditions  and  vari- 
ables have  been  stated  in  the  barest  way  possible.  •' 

In  conclusion,  let  us  notice  a  beautiful  biological 
arrangement.  If  we  compare  the  direct  with  the  in- 
direct field  with  reference  to  sensitiveness,  we  find  that 
we  are  most  sensitive  to  color  and  form  in  the  direct 
field,  and  to  light  and  movement  in  the  indirect  field. 
That  is,  we  can  see  color  and  form  most  accurately  when 
the  image  falls  upon  the  central  region  of  the  retina, 
but  we  can  detect  movements  and  changes  in  brightness 
more  readily  when  the  outer-lying  portions  of  the  retina 
are  stimulated.- 

This  is  a  story  of  adjustment  and  it  suggests  to  us 
the  real  office  of  the  indirect  field.  The  central  region 
of  the  retina,  corresponding  as  it  does  to  the  direct 
field,  is  the  organ  of  attention,  of  concentrated  mental 
activity,  which  represents  the  environment  in  terms  of 
space  and  color;  while  the  indirect  field  is  merely  ac- 
cessory. Its  functions  are  those  of  a  scout  or  guardian. 
The  life-preserving  value  of  this  arrangement  is  clear. 
Consciousness  is  warned  of  the  presence  or  approach  of 
an  object  beneficent  or  noxious  to  life,  by  impressions 
of  luminosity  or  movement  in  the  indirect  field.  If 
then  the  signal  is  heeded,  the  eye  quickly  turns  so  as 
to  bring  the  object  of  scrutiny  into  the  direct  field  where 
its  true  nature  can  be  seen  accurately,  by  the  most 
efiicient  and  economical  expenditure  of  energy. 


CHAPTER  IV 
VISUAL  SPACE 

For  One* 

Although  we  have  several  space-senses,  most  of  us 
live  predominatingly  in  a  world  of  visual  space. 
Visual  space-perception  is  therefore  one  of  the  largest 
and  most  important  topics  in  psychology.  We  shall 
limit  our  experiments  in  this  chapter  to  a  few  features 
of  visual  space  images. 

1.  Outv^ard     Projection     of     the     Visual     Image. 

a.  Floating  Flakes. — Look  toward  the  sky  with  your 
eyelids  almost  closed  and  observe  a  sort  of  snowfall 
effect.    Describe  it. 

These  flakes  are  the  shadows,  on  the  retina,  of 
particles  floating  in  the  vitreous  humor.  They  are  pro- 
jected as  objects  in  outer  space  in  accordance  with  the 
law  of  outward  projection.f 

*  This  chapter  presupposes  knowledge  of  the  structure  and 
function  of  the  eye,  as  outlined  in  the  text-books  on  psychology. 

f "  We  see  indistinct  motes  floating  about  in  the  field  of  view 
and  slowly  gravitating  downward.  Sometimes  they  are  undu- 
lating, transparent  tubes,  with  nucleated  cells  within;  some- 
times they  are  like  inextricably  tangled  threads,  or  like  matted 
masses  of  spider's  web;  sometimes  they  are  slightly  darker  spots, 
like  faint  clouds."     (Le  Conte.) 

39 


40  VISUAL  SPACE 

h.  Shadoivs  of  the  Retinal  Blood-vessels." — Stand- 
ing in  a  dark  room  with  one  eye  closed,  wave  a  candle- 
flame  or  burning  match  gently  in  a  small  circle  close 
to  the  side  and  slightly  downward  and  forward  from  the 
other  eye;  look  at  the  opposite  wall  and  you  will  see 
a  network  like  Fig.  3.t 

Describe  size,  distance,  color  if  any,  stability,  etc. 


Fig.  3. 

The  retinal  blood-vessels  enter  at  the  same  point  as 
the  ojitic  nerve  and  spread  in  a  network  inside  of 
the  retina.  As  the  rods  and  cones  lie  back  of  this  layer, 
the  blood-vessels  cast  shadows  which  become  visible 
under  the  prescribed  conditions  of  illumination.  There 
is  nothing  on  the  wall  to  correspond  to  this  system,  yet 
you  see  it  distinctly  out  there  in  space,  in  accordance 
with  the  law  of  outward  projection. 

We  are  never  directly  aware  of  the  retinal  impression. 

*  Perform  this  experiment  in  the  evening,  if  necesScary. 

f  Do  not  fatigue  tlie  eye.  Nothing  is  gained  by  straining  it.  If 
you  do  not  get  the  effect  at  once,  it  is  because  it  seems  unreason- 
able to  look  for  such  a  thing.  Look  for  a  network  like  Fig.  3, 
very  much  enlarged,  and  you  will  see  it.  The  experiment  should 
not  require  more  than  a  minute  or  two. 


1 


VISUAL  SPACE  41 

We  always  see  objects  out  in  space.  The  retinal  im- 
pression is  automatically  referred  to  its  normal  source : 
that  is  the  law  of  outward  projection.  The  history  of 
the  evolution  and  development  of  this  tendency  consti- 
tutes one  of  the  most  important  chapters  in  psychology 
as  well  as  in  the  theory  of  knowledge. 

The  conditions  of  the  above  experiments  were  un- 
usual, if  not  unnatural,  but  the  mind  responded  in  its 
habitual  way,  and  this  misdirected  tendency  revealed 
to  us  something  of  the  nature  of  the  normal  process. 
The  image  was  laid  bare,  as  it  were,  by  the  absence  of 
the  object. 

The  retinal  light  furnishes  us  another  illustration  of 
this  class  of  entoptic  phenomena.*  But  the  best  and 
most  serviceable  illustration  of  all  is  the  after-image, 
with  which  we  are  already  familiar.  It  represents  a 
physiological  condition  of  the  retina  but  is  always  seen 
out  in  space,  never  within  the  eye.f 


*  To  observe  the  retinal  light,  go  into  a  dark  room  and  cover 
your  eyes  so  as  to  shut  out  all  possibility  of  objective  light. 
Behold,  in  a  moment  you  see  a  gorgeous  array  of  colors  in  front 
of  the  eye.  They  tend  to  grow  brighter,  usually  fashion  them- 
selves into  fantastic  designs,  and  are  in  a  continual  kaleidoscopic 
commotion.  These  are  nothing  but  the  projection  of  the  local 
irritation  of  the  retina,  chiefly  through  the  circulation  of  the 
blood.  These  retinal  lights  are  the  stuft'  from  which  many  visual 
dreams  are  "made". 

f  "'Seeing  stars"  from  a  blow  or  fall  illustrates  the  same  princi- 
ple. The  story  is  told  of  a  man  who  was  attacked  and  knocked 
senseless  by  a  blow  on  the  temple  during  a  pitch-dark  night.  He 
accused  a  neighbor  whom  he  had  to  confront  in  court  with  the 
evidence,  which  was  essentially  this :  "It  was  pitch-dark,  but  the 
moment  I  felt  the  blow  there  was  a  great  flash  by  the  light  of 
which  I  saw  my  assailant."  This  may  have  been  naive  testimony: 
he  had  seen  a  light  at  the  proper  time;  he  suspected  his  neigh- 
bor; his  conviction  was  that  he  had  seen  his  neighbor. 


42  VISUAL  SPACE 

2.  The  Line  of  Projection,  a.  Projection  of  the 
After-image. — Repeat  Exp.  6,  Cli.  I. 

The  two  spatial  factors  in  the  outward  projection  are 
distance  and  direction.  We  are  here  concerned  with 
direction.  The  law  of  visible  direction  may  be  stated 
thus :  When  the  rays  from  any  radiant  strike  the  ret- 
ina, the  impression  is  referred  back  along  the  ray-line 
into  space.  The  retina  is  a  small  copy  of  the  plane  of 
projection,  a  plane  across  the  visual  field  at  right  angles 
to  the  line  of  regard.     This  is  illustrated  in  Fig.  4. 


Fig.  4. 

Every  point  in  the  plane  of  projection  has  a  correspond- 
ing point  on  the  retina.  When  the  retina  is  stimulated 
at  Cy  let  us  say,  the  image  is  referred  back  along  the  ray- 
line  c-c  and  the  object  is  seen  in  that  direction.  If  an 
area,  e.g.  6-e,  is  stimulated,  the  object  will  be  seen  in  the 
corresponding  area  e'-h'  in  the  plane  of  projection. 
The  experiment   shows  that   the   size   of  the   after- 


VISUAL  SPACE  43 

image  varies  with  the  distance  of  the  plane  of  projection. 
This  law  of  size  of  the  retinal  image  may  be  derived 
from  the  above  law  of  direction.  It  is  illustrated  by  the 
four  arrows  in  Fig.  4,  which  are  all  projections  of  the 
same  image  but  at  different  distances."^ 

h.  The  Size  of  the  Retinal  Image. — To  determine 
the  length  of  the  retinal  image  of  your  pencil  held  up- 
right at  a  distance  of  50  centimeters  in  the  line  of  re- 
gard, proceed  as  follows:  Let  the  arrow  eb\  Fig.  4, 
represent  the  pencil,  eh  its  image  upon  the  retina,  and 
n  the  nodal  point  in  a  simple  scheme  of  the  eye.  The 
two  triangles  e'h'n  and  ehn  are  similar.  The  distance 
an  in  the  normal  eye  is  about  16  millimeters;  the  dis- 
tance an  is  by  direction  50  centimeters;  you  measure 
the  length  of  the  pencil.  You  then  get  the  proportion 
e'n  :  e'h'  :  :  en  :  eh,  or  x,  the  length  of  the  retinal 
image.  Assume  that  the  retinal  image  is  on  a  flat 
surface  in  order  to  simplify  the  equation. 

c.  The  Inversion  of  the  Retinal  Image. — Make  a  pin- 
hole in  a  card  and  hold  it  toward  the  light  about  10 
centimeters  from  the  eye.  Looking  at  the  pinhole,  hold 
the  head  of  a  pin  very  close  to  the  eye,  and  in  front  of 
the  pupil,  and  observe  that  you  see  the  pin  inverted 
back  of  the  card. 

Pierce  five  pinholes  close  together  and  proceed  as 
before.     Kecord  how  many  pins  you  see. 

*To  illustrate  how  little  attention  we  pay  to  the  analysis  ot 
perceptions,  a  professor  asked  a  large  class  in  psychology  to 
estimate  how  large  the  image  of  the  moon  at  the  horizon  would 
appear  if  projected  upon  a  plane  at  arm's  length  from  the  eye. 
The  estimates  of  the  diameter  were  nearly  all  too  large;  as,  the 
size  of  a  dollar,  a  saucer,  or  a  wagon-wheel,  but  one  man  said. 
"The  size  of  a  pea,"  and  he  was  right. 


44  VISUAL  SPACE 

Examination  of  Fig.  4  showed  that  normally  all  rays 
cross  at  the  nodal  point  in  the  eye,  and  this  results  in 
the  reversal  of  the  image:  what  is  np  in  the  plane  of 
projection  becomes  down  on  the  retina;  and  what  is 
right  becomes  left.  This  is  true,  however,  only  when 
the  object  is  at  such  a  distance  that  the  rays  from  it  can 
pass  proj^erly  through  the  lens  and  form  an  image  on  the 
retina.  E'ow,  in  this  experiment,  the  pin  was  held  too 
close  to  the  eye  to  allow  a  clear  retinal  image,  and  it 
was  so  close  as  to  cast  a  good  shadow  upon  the  retina. 
This  shadow  is  not  inverted  on  the  retina,  but  it  is  pro- 
jected according  to  the  normal  law  of  visible  direction 
for  inverted  images,  and  the  result  is  that  it  is  seen  in- 
verted in  the  plane  of  projection. 

Our  normal  projection  of  the  retinal  image  is  a  habit 
based,  indeed,  upon  neural  mechanism  and  inherited 
tendency,  yet  subject  to  modification  by  training.  If 
we  should  Avear,  for  a  month,  prism  glasses  which  com- 
pletely and  consistently  reversed  the  whole  visual  field, 
we  should  in  that  time  acquire  new  habits  of  projection 
and  be  able  to  harmonize  the  reversed  retinal  images 
with  the  touch  and  movement  experiences.  Space- 
perception  is  always  a  complex  process  of  associa- 
tion and  interpretation,  though  normally  extremely 
abridged. 

d.  The  Muscular  Sensations  of  Position  of  the 
Eye. — Roll  a  sheet  of  paper  into  a  tube  one  inch  in 
diameter.  Hold  your  left  hand  about  12  centimeters 
in  front  of  your  face ;  place  the  tube  in  front  of  the  right 
eye,  lean  it  against  the  hand  and  point  it  toward  some 
distant  object.     'Now  look  wdth  both  eyes  (in  spite  of 


VISUAL  SPACE  45 

the  fact  that  the  hand  is  in  the  way  of  the  left  eye)  at 
the  distant  object  and  you  will  see  it  and  a  circular  sec- 
tion of  its  surroundings  through  a  round  hole  in  the 
palm  of  your  hand. 

So  far,  we  have  considered  the  retinal  image  as  a 
basis  for  the  perception  of  direction.  But  muscular 
impressions  of  position  and  movement  of  the  eyeball 
are  of  no  less  importance,  formally  the  two  cooperate. 
Thus,  in  perceiving  the  direction  of  a  flock  of  birds  in 
the  distance,  the  head  turns  in  the  approximate  direc- 
tion, then  the  eyeballs  turn  for  finer  adjustment  and 
sweep  back  and  forth  from  one  object  to  the  other, 
measuring  the  angular  difference  in  direction,  and 
finally  the  local  sign  *  of  the  retinal  image  indicates  the 
relative  direction  of  the  different  birds  in  the  flock. 
The  perception  of  form  is,  of  course,  merely  the  percep- 
tion of  a  complex  system  of  directions,  t 

This  experiment  illustrates  the  rigidity  of  these 
muscle-sense  marks  of  direction.  The  hole  in  the  hand 
is  clean-cut  and  absolute :  it  is  a  very  striking  illusion. 
The  local  sign  of  the  retina  is  so  rigid  and  the  position 
of  the  eyeball  is  sensed  so  accurately  that  we  see  the 
objects  upon  which  the  eyeballs  were  converged  in  the 
true  direction  in  spite  of  the  intervening  obstacle. 

*  Local  sign  is  that  special  character  of  a  sensation  whereby  we 
are  enabled  to  refer  it  to  a  particular  place,  "that  diflFerential 
quality  of  a  sensation  which  varies  with  the  part  of  the  sensitive 
surface  stimulated,  but  not  with  the  nature  of  the  stimulus." 
(Stout.) 

f  Normally  we  are  not  conscious  of  either  location  of  the  retinal 
image  or  the  sensations  of  muscular  adjustment  in  the  eye.  The 
process  of  vision  has  become  so  abbreviated  and  automatic  that  we 
merely  have  a  sort  of  direct  awareness  of  direction  without  know- 
ing why  or  how  we  become  aware  of  it. 


46  VISUAL  SPACE 

3.  Accommodation. — a.  Range  :  the  Near-point  of 
Vision. — Hold  the  point  of  a  pin  close  in  front  of  one 
eye  (the  other  eye  covered)  and  observe  that  you  can- 
not see  it  clearly.  Move  it  back  and  forth  and  find  the 
nearest  point  at  which  you  can  see  it  without  a  blur. 
That  point  is  called  the  near-point  of  vision.  Kecord 
the  distance  from  the  eye. 

If  we  are  to  have  a  clear  image  of  the  point,  the  rays 
of  light  reflected  from  that  point  must  come  to  a  focus 
upon  the  retina.  The  near-point  marks  the  limit  of 
nearness  for  which  the  lens  in  the  eye  can  adapt  itself. 
In  the  normal  eye  it  is  about  20  centimeters  frflnthe 
eye.     In  Fig.  5,  jj  represents  the  pin-point  and  r  its 


r:i-^-  r' 


Fig.  5. 

image  upon  the  retina.  If  the  pin-point  be  brought 
nearer  than  the  near-point  of  the  eye,  say  to  p,  the  rays 
from  it,  if  continued,  would  come  to  a  focus  back  of  the 
retina  at  r'  and  would  form  a  diffusion  circle  where  the 
pencil  ^V  pierces  the  retina.  This  diffusion  circle 
corresponds  to  the  blur  which  you  observed  when  the  pin 
was  too  near.  We  can  see  objects  clearly  only  when 
they  lie  at  or  beyond  the  near-point. 

Xear-sighted  persons  also  have  a  far-point  beyond 
which  objects  blur  because  the  lens  cannot  adapt  itself 
to  that  distance.  But,  in  the  normal  eye,  this  point  is  at 
infinite   distance;   i.e.,   the   eye   can   accommodate   for 


VISUAL  SPACE  47 

parallel  rays.     The  range  between  the  near-point  and 
the  far-point  is  called  the  range  of  accommodation. 

h.  Line  of  Accommodation. — Pierce  two  pinholes, 
about  1  millimeter  apart,  in  a  card.  Stick  two  pins 
through  a  sheet  of  paper,  20  centimeters  apart.  Cover 
one  eye  and  hold  the  card  close  in  front  of  the  other  eye 
so  that  the  two  holes  are  in  a  horizontal  position  and  fall 
within  the  circumference  of  the  pupil;  hold  the  paper 
with  the  pins  pointing  upward  so  that  the  near  pin 
is  20  centimeters  from  the  eye  and  the  two  pin-points 


are  in  the  same  line  of  regard.  Observe  that,  when 
you  accommodate  for  the  near  pin,  it  is  clear,  but  the 
distant  one  is  double ;  and  when  you  accommodate  for 
the  distant  pin,  it  is  clear  and  the  near  one  is  double. 
Take  out  the  distant  pin  and  move  it  toward  the  near 
one  and  find  how  close  you  must  bring  it  before  you  can 
see  both  clearly  with  a  single  accommodation.*  Kecord 
this  distance,  which  is  called  the  line  of  accommodation. 
Fig.  6  represents  the  accommodation  for  the  near 
pin,  and  Fig.  7  the  distant.     Write  out  a  full  explana- 

*  Make  sure  that  both  holes  are  in  front  of  the  pupil.     Work 
with  precision  and  a  purpose  and  you  will  not  strain  the  eye! 


48 


VISUAL  SPACE 


tion  of  each  figure,  assuming  that  A  and  B  represent 
the  two  pins. 

Strictly  the  eye  can  accommodate  for  only  one  point 
in  distance  at  a  time.  All  points  in  front  of  and  behind 
that  point  must  appear-  blurred.  This  can  be  verified 
rougldy  by  looking  systematically  with  one  eye  along  a 
row  of  objects  in  the  line  of  regard.  Looking  through 
the  two  pinholes  has  the  advantage  of  simplifying  the 
situation  by  producing  two  images  instead  of  a  blur. 
If  there  were  more  holes,  there  would  be  more  images. 


Fig.  7. 

Practically,  however,  the  two  pins  may  be  separated 
by  a  considerable  distance  and  yet  both  be  seen  single  or 
clear  with  the  same  compromise  accommodation  because 
^'they  seem  clear  enough."-  We  must  therefore  speak 
of  a  line  of  accommodation  ratlier  than  a  point.  We 
can  see  two  or  more  objects  clearly  at  the  same  time 
only  if  they  lie  within  the  line  of  accommodation. 

4.  Convergence:  Double  Images. — a.  Doubling  the 
Distant  Object. — Hold  two  objects  such  as  a  pen  and  a 
pencil  in  the  same  line  of  regard,  the  former  about  20 
and  the  latter  about  40  centimeters  away  from  the  eyes. 
Fixate  the  point  of  the  pen  and,  wdiile  the  eyes  are  thus 


VISUAL  SPACE  49 

converged,  observe  that  you  see  two  pencils.  Close  one 
eye  at  a  time  and  determine  which  of  the  double  images 
belongs  to  each  eye.  Eecord  to  which  eye  each  image 
belongs,  the  distance  between  the  double  images,  and  the 
position  of  the  double  images  with  reference  to  the 
actual  position  of  the  pencil. 

Write  explanation  of  Fig.  8,  which  illustrates  this.* 


Fig.  8. 

Our  two  eyes  constitute  an  effective  mechanism  for 
the  perception  of  distance  or  relief.  One  of  the  limita- 
tions which  follows  from  the  very  efficiency  of  the 
mechanism  is  that  we  can  see  only  one  point  in  distance 
clearly  at  a  time ;  every  object  nearer  or  farther  away 
than  this  point  must  be  seen  double  if  attended  to. 


*  The  level  of  the  horizontal  line  L-R  is  somewhat  arbitrary, 
expect  that  it  must  lie  between  p  and  p'.  If  the  observer  had 
not  knoA\Ti  the  actual  distance  of  the  pencil  he  would  probably 
have  seen  it  at  about  the  same  distance  as  the  pen;  but,  know- 
ing the  actual  distance,  there  is  a  tendency  to  see  the  double 
images  at  approximately  the  true  distance.  The  level  chosen 
in  the  diagram  represents  a  compromise. 


50  VISUAL  SPACE 

This  experiment  has  demonstrated  that  fact  as  regards 
an  object  beyond  the  fixation-point.  The  next  experi- 
ment demonstrates  it  for  objects  nearer  than  the  fixation- 
point,  and  the  experiment  following  that  proves  in  a 
most  general  way  that  all  points  within  the  line  of 
vision,  which  are  nearer  or  more  remote  than  the  fixa- 
tion-point are  seen  double. 

b.  Doubling  the  Near  Object. — With  pen  and  pencil 
as  before,  fixate  the  pencil  and,  wdiile  the  eyes  are  thus 
converged,  observe  that  you  see  two  pens.    Close  one  eye 


Fig.  9. 

at  a  time  to  identify  the  double  images  and  record  as  in 
Exp.  4  a.  Write  explanation  of  Fig.  9,  which  illus- 
trates this.* 

c.  Doubling  of  all  Points  except  the  Fixation-point. — 
Stick  a  pin  into  a  pencil  at  the  middle,  point  the  pencil 

*  The  double  images  of  objects  nearer  than  the  point  of  fixa- 
tion are  said  to  be  "crossed,"  while  those  of  objects  beyond  the 
point  of  fixation  are  "uncrossed."     Titchener  gives  the  mnemonic: 
"Remote  regard  reverses; 
Nearer,  notice,  not." 


VISUAL  SPACE  61 

straight  forward  and  fixate  the  pin ;  observe  that  you  see 
two  pencils  forming  an  X,  with  the  crossing  at  the  pin. 
Close  one  eye  at  a  time  and  observe  that  the  law  of 
crossed  and  imcrossed  images  is  verified. 

Practically,  again,  this  point  of  clear  vision  in  con- 
vergence is  really  a  line  which  we  might  by  analogy  call 
the  line  of  convergence.  Experiments  with  fine  points 
show  that  within  a  moderately  near  range  it  is  really  a 
point,  for  one  of  two  pin-points  will  double  until  they 
come  together,  but  as  we  recede  the  possible  separation 
becomes  appreciable,  although  the  ''line  of  convergence" 
is  relatively  much  shorter  than  the  line  of  accom- 
modation. 

d.  Double  Images  in  Indirect  Vision. — Hold  pen  and 
pencil  as  in  Exp.  4  a;  fixate  the  pen  (near)  and  observe 
how  far  you  can  move  the  pencil  to  the  right  from  the 
line  of  vision  before  one  of  the  double  images  of  the 
pencil  disappears.     Kecord  five  trials. 

It  becomes  more  and  more  difficult  to  perceive  the 
double  images  as  we  pass  the  object  gradually  into  the 
indirect  field.  One  of  the  double  images  can  be  seen 
far  beyond  where  the  two  can  be  seen.  In  this  case 
it  is  the  right-eye  image,  as  can  be  demonstrated  by 
closing  one  eye  at  a  time. 

e.  Doubling  Numerous  Objects. — Double  a  strip  of 
paper  and  stick  a  row  of  five  pins  through  it  about  1 
centimeter  apart.  Hold  the  paper  in  a  horizontal  posi- 
tion at  arm's  length  and  at  right  angles  to  the  line  of  re- 
gard; fixate  the  eyes  upon  the  pen-point,  held  midway 
between  the  eyes  and  the  pins,  and  count  the  pins. 
Record  number. 


52  VISUAL  SPACE 

All  objects  outside  of  the  ''line  of  convergence' ' 
double  Avhen  seen  with  both  eyes.*  Why,  then,  do  we 
see  single  objects  in  nature  and  elsewhere  when  many 
objects  outside  of  the  line  of  convergence  are  seen  at 
the  same  time  ?  First,  we  pay  attention  to  only  one 
point  at  a  time ;  the  eyes  shift  with  the  greatest  rapidity 
from  point  to  point  and  make  snapshots  which  we  are 
aware  of  only  as  a  composite  view.  Second,  the  utility 
of  disregarding  double  images  has  resulted  in  a  natural 
capacity  for  ''counting"  only  the  impressions  which 
favor  single  vision.  The  fact  that  the  single  eye  can 
get  a  fully  satisfactory  image  only  at  the  fovea  favors 
this  discarding  of  other  images.  And,  third,  a  complex 
view  is  never  clear. 

But  why  do  we  see  single  objects  at  all  from  two 
images  ?  Like  the  projection  of  the  single  image  (in- 
deed it  is  a  part  of  the  process),  the  identifying  of 
images  which  fall  upon  corresponding  points  of  the  two 
retinse  has  been  learned  through  race  and  individual 
experience  in  associating  sight  with  touch  and  move- 
ment. 

/.  DouhUng  Complex  and  Large  Objects. — Hold  one 
or  more  postage-stamps  or  other  complex  objects  at 
arm's  length  and  observe  by  near  fixation,  as  in  Exp. 
4  h,  or  far  fixation,  as  in  Exp.  4  a,  that  the  whole  ob- 
jects double.  Try  larger  objects,  such  as  a  letter  or  a 
wall-picture. 

*  The  indirect  field,  Exp.  4  d,  is  no  exception,  because  when 
one  of  the  double  images  disappears  we  see  only  with  one  eye. 

Of  course,  the  doubling  is  always  in  the  line  of  the  eyes, 
normally  the  horizontal — the  whole  paper  strip  doubled,  but 
lengthwise. 


VISUAL  SPACE  53 

Embody  the  results  of  these  six  experiments  on  double 
images  in  binocular  vision  in  one  general  law  and  write 
it  out. 

5.  Relief. — a.  Similai'  Images. — Look  at  Fig.  3,  with 
one  eye  at  a  time,  and  observe  that  the  two  images  are 
similar  and  there  is  no  relief. 

h.  Disparate  Images.- — Hold  the  closed  text-book 
erect  and  with  the  back  toward  you  at  arm's  length ;  look 
at  it  first  with  one  eye  and  then  with  the  other  and 
observe  that  the  two  images  are  disparate,  i.e.,  unlike. 
Look  with  both  eyes  and  observe  that  you  see  the  book 
in  relief. 

The  basis  for  the  perception  of  relief  lies  in  the  dis- 
parateness of  the  two  images.  Relief  is  a  mental  syn- 
thesis based  upon  two  independent  series  of  sense  data 
which  become  harmonized  through  the  relief-interpreta- 
tion. The  mind  interprets  each  image  as  a  different 
view  of  the  same  object.  Look  again  at  the  book  and 
observe  how  the  two  disparate  views  supplement  each 
other,  blend  and  are  satisfied  in  the  appropriate  com- 
bination. Knowing  the  character  of  the  difference 
between  two  images  and  the  degree  of  convergence,  we 
can  predict  the  relief.  This  is  well  illustrated  in 
stereoscopic  vision. 

6.  Stereoscopic  Vision. — Eoll  a  piece  of  paper  into 
a  truncated  cone  and  trim  it  to  a  diameter  of  8  centi- 
meters at  the  base  and  2  centimeters  at  the  frustum,  and 
make  it  about  6  centimeters  high.  Pin  it  together  and 
set  it  up  about  50  centimeters  away,  with  the  frustum 


64  VISUAL  SPACE 

facing  you  at  the  level  of  your  eyes.  Look  at  it  with 
the  two  eyes  alternately  and  observe  the  disparateness 
of  the  two  images. 

Draw  the  diameters  of  the  two  ends,  for  each  eye 
separately,  as  they  would  be  projected  on  a  pane  of 
glass  held  about  15  centimeters  in  front  of  the  eyes. 
When  this  drawing  is  seen  in  a  stereoscope  it  should 
give  the  true  skeleton  of  the  cone.* 

There  are  two  fundamental  conditions  of  stereo- 
scopic vision :  first,  that  the  two  views  shall  differ  so 
as  to  produce  the  appropriate  disparateness  in  the  two 
retinal  images;  and,  second,  that  the  two  views  shall 
be  seen  with  the  two  eyes  converged  upon  one  point. 
The  drawings  provide  the  first ;  the  lenses  in  the  stereo- 
scope, or  converging  for  a  point  back  of  the  card  with- 
out the  stereoscope,  provide  for  the  second,  t 

*  With  a  little  practice  stereoscopic  views  may  be  seen  in  re- 
lief without  the  use  of  the  stereoscope  by  merely  converging  the 
eyes  upon  a  point  at  a  suitable  distance  back  of  the  card. 
Try  it. 

f  One  of  the  best  elementary  treatments  of  this  topic,  visual 
space,  is  found  in  Witmer,  "Analytical  Psycholog}^"  Ch.  IV. 


CHAPTEE  V 
AUDITOEY  SPACE 

For  Two* 
There  are  three  aspects  of  the  problem  of  auditory 
space ;  namely^  direction,  distance,  and  volume.     The 
present  chapter  is  devoted  to  the  problem  of  hearing  the 
direction  of  sound. 

The  experiments  in  this  chapter  should  be  helpful  in 

answering  such  questions  as:  Is  the  ear  a  space-sense 

organ  ?     How  do  we  perceive  the  direction  of  sound  by 

hearing  ?    What  are  some  of  the  laws  of  localization  ?  f 

Produce  the  sound,  which  is  to  be  localized,  by  snap- 

*  These  experiments  must  be  performed  at  some  other  time 
than  during  the  class  period,  unless  there  is  opportunity  for 
the  class  to  scatter  into  different  rooms  or  out  of  doors.  Two 
students  must  work  together;  the  one  who  manipulates  the  ap- 
paratus is  called  the  experimenter,  ( E ) ,  and  the  one  on  whom 
the  experiment  is  performed  is  called  the  observer,  (0).  Each 
takes  turn  as  E  and  0  for  each  experiment.  E  always  keeps 
the  record  obtained  as  experimenter;  thus  each  preserves  the 
record  of  the  other.  O  should  be  blindfolded  and  seated  com- 
fortably in  such  a  position  that  he  can  hold  his  head  erect  and 
steady  in  a  given  position  during  an  experiment. 

f  There  is  difference  of  opinion  as  to  whether  or  not  the  ear 
is  a  space-sense  organ.  Those  who  hold  that  it  is  not  a  space- 
sense  organ  base  their  opinion  largely  upon  two  anatomical  facts: 
( 1 )  that  the  portion  of  the  ear  which  is  the  organ  of  hearing 
possesses  no  spread-out  surface  such  that  an  arrangement  of 
stimulations  upon  it  may  represent  the  spatial  relations  of  the 
external  world;  and  (2)  that  the  ear  is  unprovided  with  a  mus- 
cular apparatus  for  focusing  itself  for  different  directions.  In 
these  respects  the  ear  is  contrasted  with  the  visual  and  tactual 
arrangements  for  perception  of  space. 

It  is  also  well  to  bear  in  mind  the  chief  theories  of  localiza- 

55 


56  AUDITOEY  SPACE 

ping  two  coins.*  Place  one  coin  on  each  side  of  the 
forefinger  and  press  them  together  with  the  thumb  and 
the  forefinger  until  they  slide  together  with  a  snap. 
Shift  the  coins  deftly  from  one  hand  to  the  other  and 
avoid  swaying  movements  of  the  body  and  rustling  of 
the  garments.  Stand  on  the  side  and  reach  out  both 
arms  symmetrically.     Blindfold  and  seat  the  observer. 

1.  Radially  in  the  Median  Plane,  f — Let  it  be  under- 
stood that  the  sound  may  come  from  any  of  the  seven 
directions  45°  apart:  up,  up-front,  front,  down-front, 
down-back,  back,  and  up-back,  all  within  the  median 
plane.     Produce  the  sound  three  times  in  each  of  these 

tion.     These  may  be  divided  into  five  classes: 

(a)  The  intensity  theory.  The  difference  in  the  strength  of 
the  sound  in  the  two  ears  is  the  basis  for  the  hearing  of  direction. 

(h)  The  tactual  theory.  Sound  vibrations  also  give  rise  to 
sensations  of  touch,  and  we  confuse  these  touch  sensations  with 
sound  sensations. 

(c)  Semicircular-canal  theories.  The  semicircular  canals  in 
the  ear  are  special  organs  for  the  sensing  of  direction. 

{d)  Original  space  differences  in  the  sensations  of  the  two 
ears. 

(e)  The  intensity-quality  theory.  Both  quality  and  intensity 
aid  in  the  perception  of  direction. 

At  the  end  of  this  chapter  we  shall  turn  back  and  ask  which  of 
these  theories  has  been  supported. 

*The  following  are  better  sources  of  sound  if  available:  (1)  a 
telephone  receiver  in  circuit  with  a  battery  and  a  mercury  key; 
(2)  a  "frog  snapper"  (electric  supply  houses,  25  cents)  ;  or  (3)  a 
paper  clip  such  as  is  used  in  hanging  placards. 

The  apparatus  which  is  used  for  accurate  work  in  the  labora- 
tory is  called  a  sound-perimeter  or  sound-cage.  It  is  so  con- 
structed that  the  experimenter  can  manipulate  it  from  one  point 
in  the  room  without  moving  around.  It  enables  him  to  vary  the 
direction,  the  distance,  the  kind,  the  strength,  the  pitch,  and 
the  complexity  of  the  sound;  to  control  these  conditions;  and 
to  make  accurate  measurements. 

fThe  median  plane  is  that  vertical  plane  which,  passing 
through  the  body,  divides  it  into  right  and  left  symmetrical 
halves. 


AUDITOKY  SPACE  57 

directions,  at  a  distance  of  about  50  centimeters,  measur- 
ing from  the  center  of  the  head.  Distribute  the  trials 
approximately  as  they  might  run  by  chance.  Eequire 
O  to  say  in  which  of  the  seven  directions  he  hears  the 
sound.  "^  Eecord  each  answer  under  the  appropriate 
heading  in  a  prepared  tabular  form.  Figure  how  many 
answers  out  of  the  21  are  right,  and  how  many  are  45°, 
90°,  135°,  and  180°  wrong  respectively. 

Exp.  1  might  well  have  been  entitled  the  ^^inability 
to  localize  sound."  The  observer  is  very  much  sur- 
prised and  discouraged  when  he  sees  his  record. 

There  are  two  factors  in  the  record,  the  number  of 
correct  localizations  and  the  magnitude  of  the  incorrect 
localizations,  to  be  considered.  As  there  are  21  trials 
distributed  equally  among  7  points,  three  of  the  locali- 
zations would  be  right  by  pure  chance.  The  trials  are 
not  sufficiently  numerous  to  enable  us  to  apply  the  laws 
of  chance  in  prediction,  but  extensive  experiments  show 
that  a  few  more  localizations  than  can  be  accounted  for 
by  chance,  will  be  right,  probably  less  than  10  per  cent. 
On  that  basis,  the  observer  might  have  four  or  five 
correct  localizations  in  this  experiment. t 

*It  is  of  the  greatest  importance  that  O  should  have  no  other 
means  of  detecting  direction  than  by  hearing.  E  must  therefore 
take  every  possible  precaution  to  avoid  giving  any  suggestion  or 
clue   by  word,  situation,  or  movement. 

Of  course,  the  experimenter  will  be  shrewd  enough  to  give 
no  intimations  to  the  observer  about  his  errors  during  the  prog- 
ress of  the  experiment. 

f  If  the  observer  gave  more  than  one-fourth  of  the  localizations 
correctly,  it  is  probable  that  this  was  due  to  failure  on  the  part 
of  the  experimenter  to  snap  the  coins  exactly  in  the  median  plane, 
or  to  eliminate  accessory  sounds  from  his  own  movements,  breath- 
ing, etc.  Creaking  sounds  from  the  coat-sleeve  are  often  taken 
as  a  cue. 


58  AUDITORY  SPACE 

The  other  factor,  the  degree  of  error  in  the  misplace- 
ments, is  equally  significant.  Under  strict  experi- 
mental conditions  the  observer  is  almost  as  liable  to 
make  an  error  of  180°  as  of  45°  misplacement."^ 

If  the  same  stimulus  is  used,  a  person  can  improve 
in  this  localization ;  but  the  improvement  will  be  almost 
entirely  lost  as  soon  as  the  kind  of  sound  and  the 
strength  of  sound  are  varied. 

It  is  a  striking  fact  that  the  observer  has  undue  con- 
fidence in  his  ability.  When  he  said  ^'up-front"  he 
heard  the  sound  distinctly  there,  although  it  may  have 
come  from  any  other  point.  This  illusion  of  certainty 
is  characteristic  of  all  our  hearing  of  direction.  We 
continually  either  misjudge  the  direction,  or  learn  the 
direction  through  other  means  than  hearing;  yet  we 
have  a  distinct  feeling  that  we  have  heard  the 
direction,  t 

2.  Horizontally  in  Front — Measure  the  discrimi- 
native sensibility  for  direction  of  sound  in  a  horizontal 
plane  in  front,  at  the  level  of  the  ears.  Proceed  as  fol- 
lows: Mark  a  stick  about  50  centimeters  long  into  3- 
centimeter  steps,  beginning  at  the  middle,  and  marking 

*  This  inability  to  localize  sounds  in  the  median  plane  was  dis- 
covered by  Lord  Rayleigh  in  1875.  The  inability  is  peculiar  to 
this  plane,  and  therefore  has  great  significance  as  a  test  of 
theories, 

f  Sitting  near  the  central  aisle  of  the  Fifth  Avenue  Cathedral, 
New  York,  and  looking  straight  forward,  it  is  practically  im- 
possible to  tell  whether  the  organ-tones  issue  from  the  front 
or  back  of  the  cathedral.  If  we  could  see  the  organ,  the  matter 
would  be  different.  One  of  the  reasons  that  this  inability  does 
not  disturb  us  much  is  that,  when  there  is  no  correlation  in  the 
other  senses  or  in  reason,  we  remain  uncorrected  in  the  illusion 
of  having  heard  the  direction  rightly. 


AUDITOKY  SPACE  69 

symmetrically  in  both  directions.  Seat  O  as  in  Exp.  1. 
Hold  the  stick  1  meter  from  the  center  of  his  head, 
directly  in  front,  in  a  horizontal  position,  at  right  angles 
to  the  median  plane,  and  at  the  level  of  his  ears. 
Sound,  in  quick  succession,  two  clicks — the  first,  or 
standard,  sound  directly  in  front  (at  the  middle  or  0° 
of  the  stick)  and  the  second,  or  compared,  click  on  either 
side  of  the  standard,  the  order  of  sides  to  be  practically 
such  as  would  follow  from  chance.  Require  O  to  say 
whether  the  second  sound  was  to  his  right  or  left.  Start 
with  a  distance  of  3  centimeters  between  the  standard 
and  compare  sounds  and  repeat  the  trials  until  O 
makes  a  mistake  or  has  ten  successive  answers  right. 
If  a  mistake  is  made,  try  with  a  distance  of  6  centi- 
meters in  the  same  way.  Continue  thus,  trying  succes- 
sive larger  steps,  increasing  each  time  by  3  centimeters, 
until  you  have  reached  one  for  which  O  gives  ten  suc- 
cessive correct  answers.  Record  the  number  of  right 
answers  for  each  step. 

3.  Horizontally    at    the     Back. — Make    the     same 

measurement  as  in  Exp.  2,  for  the  symmetrical  position 
at  the  back  of  O.  In  this  and  the  following  experi- 
ments, E  should  retain  the  same  position,  and  O  should 
turn  around  in  order  to  have  the  resonance  in  the  room 
constant. 

4.  Horizontally  at  the  Side. — Make  the  same 
measurement  as  in  Exp.  2  for  a  point  in  the  hori- 
zontal plane  at  the  level  of  the  ears  and  1  meter  directly 
to  the  right  of  the  center  of  O's  head.  Let  0  answer 
^'forward''  or  '^backward.'' 


60 


AUDITORY  SPACE 


5.  Vertically  at  the  Side. — From  the  same  position 
as  in  Exp.  4,  but  in  the  vertical  plane,  make  the  same 
measurement  as  in  Exp.  2 
^'down.'' 


Let  O  answer  ^'up"  or 


6.  Introspections. — Repeat  the  largest  step  in  Exp. 
4  deliberately  a  number  of  times  and  allow  O  to  study 
and  describe  the  subjective  differences  of  the  sounds  by 
which  he  judges  their  direction.  Record  in  full  his 
observations  on  differences  in  intensity,  quality,  dis- 
tance,   tactual    sensations,    motor    tendencies,    visual 


Qlfi    ',5;° 


0°B   15°    30 


Fig.  10. 


imagery, — in  short,  all  features  which  seem  to  result 
from  change  in  the  direction  of  the  sound. 

The  last  five  experiments  may  be  discussed  together 
most  profitably.  Fig.  10  is  the  record  of  the  localiza- 
tions of  a  trained  observer  within  the  right  half  of  the 
horizontal  plane  at  the  level  of  the  ears.  It  is  based 
upon  18,000  measurements  under  the  most  favorable 
conditions  and  therefore  has  a  high  degree  of  validity. 
The  radii  show  the  directions  and  the  arcs  represent  the 


AUDITORY  SPACE  61 

distance  between  the  standard  and  the  compared  sound 
which  will  yield  75  per  cent  of  right  judgments.*  As 
the  sounds  were  produced  1  meter  from  the  center  of  the 
head,  each  degree  corresponds  to  17.5  millimeters. 
Thus  the  curve  shows  a  limit  of  .9°  at  0°  F  (our  Exp. 
2),  1°  at  0°  B  (our  Exp.  3),  and  4.5°  at  the  right  (our 
Exp.  4). 

In  general,  then,  the  law  which  should  stand  as  the 
prediction  of  our  results  is  that  the  localization  in  this 
horizontal  plane  is  poorest  at  the  side,  improves  by  three 
large  steps  in  front  and  three  behind  in  passing  toward 
the  median  plane ;  it  is  about  equally  fine  for  front  and 
back,  and  it  is  more  than  four  times  as  delicate  for  these 
points  as  for  the  side. 

Curves  of  this  kind  have  been  worked  out  for  repre- 
sentative planes  in  the  field  of  space  around  the  head. 
The  results  of  some  of  these  are  shown  graphically  in 
Fig.  11,  wdiich  represents  the  right  hemisphere.  Ob- 
serve that  the  first  vertical  at  the  left  stands  for  the 
front  half  of  the  median  plane,  and  the  first  vertical  at 
the  right  represents  the  back  half  of  the  same  plane, 
and  that  the  other  vertical  lines  represent  intervening 
meridians  at  intervals  of  15°  on  the  surface  of  a  hemi- 
sphere centered  at  the  observer's  head  and  lying  toward 

*  In  laboratory  experiments  it  is  customary  to  use  the  dif- 
ference which  is  calculated  to  yield  75  per  cent  of  correct  judg- 
ments as  the  measure  of  the  discrimination.  In  the  present  ex- 
periments we  have  adopted  the  much  higher  standard  of  100  per 
cent  correct  judgments,  partly  to  shorten  and  simplify  the 
method,  and  partly  to  avoid  computations.  Of  course,  the  rec- 
ords for  our  experiments  will  therefore  be  correspondingly 
larger.  They  are  also  larger  on  account  of  the  observer's  lack 
of  training,  but  they  should  express  the  above  general  tendency 
equally  well. 


62 


AUDITORY  SPACE 


his  right.""      The  middle  horizontal  line  represents  the 
one  in  which  our  Exps.  4  and  5  are  located ;  above  and 


-(> 


() — () — () — ®-^^■ 


^^-^^ 


<HH 


15        30        «RF    Tso        75        90R     ^ /5       60        45Ra     30        ,5 


i) — e — e — ^^— O— () — () — () — (^ 


Fig.  11. 

below    this    the    parallel    horizontal    lines    represent 
meridians  at  the  respective  latitudes  marked. 

The  little  figures  may  be  called  sensory  ellipses  in 
auditory  space  discrimination.     They  are  constructed 

*In  reality  these  converge  to  one  point  at  the  top  and  one 
point  at  the  bottom ;  the  top  and  bottom  lines  become  single  points 
within  the  median  plane.  They  are  projected  in  the  present  man- 
ner in  order  to  show  the  relative  dimensions  of  the  ellipses. 


AUDITORY  SPACE  63 

in  the  following  manner:  At  any  intersection,  vertical 
and  horizontal  distances  are  laid  off  on  the  basis  of  the 
corresponding  measurements.  Thus,  if  the  measure 
of  the  discriminative  ability  is  5°,  the  points  are  laid  off 
2  1-2°  below  and  2  1-2°  above  the  intersection.  Two 
points  are  laid  off  on  the  horizontal  line  on  the  same 
principle.  An  ellipse  is  then  constructed  with  these 
points  as  the  termini  of  the  two  diameters. 

The  ellipses  mean  that  every  diameter  represents,  on 
the  scale  of  the  chart,  the  degree  of  separation  of  two 
sounds  which  would  yield  75  per  cent  correct  judgments 
of  direction  under  the  given  conditions  of  the  ex- 
periments. * 

Thus,  following  the  middle  horizontal  line,  0°  F, 
0'  B,  and  90°  R  represent  the  points  in  Fig.  10  which 
correspond  to  our  measurements  in  Exps.  2,  3,  and  4 
respectively.  Exp.  5  is  represented  on  the  vertical 
axis  at  90°  E.  This  ellipse  shows  that  at  this  point  our 
discrimination  is  keener  in  the  horizontal  direction  than 
in  the  vertical. 

The  psychologist  can  lay  out  a  plot  of  the  acoustic 
field,  represent  measurements  of  significant  distances 
and  directions  upon  it,  trace  their  laws  and  distributions 
and  tell  why  the  features  represented  have  taken  these 
particular  forms.  And  furthermore  he  can  give  his 
chart  of  the  acoustic  field  to  the  world  as  a  guide  in  the 
attempt  to  hear  direction,  and  as  a  criterion  of  the 
validity  of  purported  hearing  of  direction. 

The  introspections  in  Exp.  6  bring  out  a  number  of 

*  Where  there  are  only  two  dots  and  no  ellipse,  the  measure 
ments  have  not  been  made  for  the  other  diameter. 


64  AUDITORY  SPACE 

interesting  subjective  factors.  Some  of  them  may  be 
predicted. 

The  sound  seems  to  be  strongest  at  the  aural  axis. 
This  in  turn  makes  the  sounds  which  are  at  the  aural 
axis  seem  nearer  than  those  which  are  away  from  it; 
these  sounds  are  also  richer  and  clearer. 

There  is  also  a  tendency  to  hear  the  forward  sound  as 
higher  and  the  backward  sound  as  lower  in  pitch  than 
the  standard  sound.  The  most  interesting  and  compli- 
cated observations  probably  refer  to  misplacements: 
the  observer  knows  that  the  sound  comes  from  a  given 
point,  but  he  hears  it  in  some  other  direction.  These 
misplacements,  in  a  careful  observer,  follow  definite 
laws,  which  may  be  worked  out,  as  many  of  them  already 
have  been. 

Most  observers  have  distinct  visual  imagery  for  the 
movements  of  the  sounding  body.  Frequently  one  is 
conscious  only  of  this  mental  vision,  and  the  sound 
changes  as  interpreted  in  terms  of  sight.  The  observer 
says  that  the  sound  is  forward  because  he  has  a  mental 
picture  of  the  sounding  body  in  that  position.  I^early 
all  observers  make  automatic  movements  in  adaptation 
to  the  changes  in  direction  of  the  sound,  and  may  be 
conscious  of  these  movements  and  be  guided  by  them 
without  being  aware  of  their  auditory  basis.  Mental 
images  of  movement  or  tendencies  to  movement  are  also 
prominent.  One  may  detect  images  of  strain  and 
movement  which  vary  with  the  direction  of  the  sound. 

Among  the  numerous  tendencies  which  affect  localiza- 
tion are  the  following: 

There  is  a  tendency  to  locate  every  median  sound  in 


AUDITOKY  SPACE  65 

the  upper  front  quarter,  by  the  force  of  habit.  Like- 
wise sounds  at  the  level  of  the  ears  are  usually  mis- 
placed upward,  and  sounds  in  the  vertical  plane  through 
the  aural  axis  are  usually  misplaced  forward. 

The  effect  of  expectation  is  exceedingly  complicated. 
Thus,  we  tend  to  hear  a  sound  from  the  direction  it  is 
expected ;  but  if  the  direction  is  sensibly  different,  there 
is  a  tendency  to  overestimate  this  difference.     Try  it. 

There  is  a  tendency  to  turn  the  eyes  in  the  direction 
of  attention,  and  this  turning  of  the  eyes  influences  the 
perception  of  direction. 

The  hearing  of  direction  is  a  neglected  capacity.  We 
ordinarily  depend  upon  sight ;  but  should  the  exigencies 
of  life  demand  it,  we  could  improve  very  much  in  the 
hearing  of  direction. 

Two  ears  are  necessary  for  the  normal  hearing  of 
direction,  but  certain  localizations  are  possible  with  one 
ear  alone.  Fig.  12  is  the  curve  of  localization,  in  the 
same  plane  as  is  represented  by  Fig.  10,  for  a  person 
who  hears  only  with  the  right  ear.  It  shows  that  hear- 
ing of  direction  is  keenest  opposite  the  ear  which  is 
intact  and  gradually  decreases  both  in  front  and  behind 
to  a  point  of  poorest  hearing  in  a  symmetrical  point  on 
the  other  side.  Thus,  he  detects  a  difference  of  4° 
opposite  the  good  ear,  but  there  has  to  be  a  difference  of 
21.6°  opposite  the  deaf  ear.  ^Note  the  bearing  of  this 
upon  a  theory.     The  dotted  curve  is  a  copy  of  Fig.  10. 

It  is  probable  that  pure  tones  cannot  be  localized  at 
all  by  one  ear  alone. 

Difference  in  the  keenness  of  the  two  ears  leads  to 
misplacements  whenever  the  decline  or  restoration  of 


66 


AUDITOKY  SPACE 


hearing  in  one  ear  is  sudden.  When  the  loss  or  restora- 
tion is  gradual,  Ave  adapt  ourselves  to  it. 

There  are  numerous  systems  of  confusion-points; 
that  is,  two  points  in  different  quarters  which  have  the 
same  ''local  sign"  so  that,  although  far  apart,  the  sounds 
from  these  two  sources  cannot  be  distinguished.  Thus 
45°  right-back  and  45°  right-front  are  often  confused. 

Every  unnatural  position  of  the  body,  or  part  of  the 
body,  tends  to  produce  errors  in  localization.     For  ex- 


FiG.  12. 


ample,  if  the  head  is  turned  to  the  right,  a  sound  will 
be  slightly  misplaced  in  the  direction  in  which  the  head 
is  turned. 

It  is  usually  supposed  that  a  soimd  cannot  be  heard  as 
well  from  behind  as  from  the  front.  But  experiments 
show  that  we  can  hear  just  as  faint  a  sound  from  the 
back  as  from  the  front.  Still  the  common  suj)position 
leads  to  many  misplacements. 

Our  hearing  is  keenest  directly  opposite  each  ear  and 
it  decreases  gi-adually  toward  the  median  plane  both  in 
front  and  back.     Intensity  of  sound  may  therefore  be 


AUDITORY  SPACE  67 

interpreted  in  terms  of  direction;  it  is  possible  to  pre- 
dict an  apparent  change  in  direction  from  the  mere  vary- 
ing of  the  intensity  of  the  sound. 

Other  things  being  equal,  the  fainter  sound  is  judged 
to  be  more  distant. 

Timbre  is  the  characteristic  quality  of  a  sound  and 
depends  upon  the  presence  and  reinforcement  of  over- 
tones. The  difference  between  the  tones  of  the  various 
musical  instruments  is  chiefly  a  difference  in  timbre. 
As  a  rule,  the  richer  the  tone  the  better  it  can  be 
localized.  The  human  voice  in  normal  speech  can  be 
localized  better  than  any  other  sound.  The  localization 
of  the  sound  of  a  tuning-fork  is  very  much  inferior  to 
that  of  the  voice ;  and  some  contend  that  a  simple  pure 
tone  cannot  be  localized  at  all.  At  any  rate,  the  richer 
the  tone  the  more  ''ear-marks''  of  direction  it  can 
have. 

The  longer  a  sound  lasts  within  certain  limits,  the 
better  it  is  localized. 

By  introducing  a  funnel  into  the  ear  and  turning  it  in 
different  directions,  one  can  make  the  same  sound  seem 
to  come  from  different  places. 

The  resonance  and  similar  modifications  of  the  sound 
by  the  environment  are  familiar  sources  of  disturbance 
to  localization.  If  the  experiments  are  made  indoors, 
they  should  preferably  be  made  near  the  center  of  a 
relatively  empty  cubical  room. 

There  are  exceedingly  interesting  phenomena  of 
sound  fusions.  'No  matter  how  many  sounds  are  pro- 
duced simultaneously,  no  matter  from  what  different 
directions  they  may  come,  provided  the  sounds  are  of 


68  AUDITORY  SPACE 

the  same  kind  and  pitch,  they  will  be  heard  as  one.  A 
very  pretty  experiment  is  to  connect  two  telephone  re- 
ceivers to  the  same  tuning-fork  so  that  the  same  tone 
is  produced  in  both  receivers.  The  two  tones  will  in- 
variably be  heard  as  one,  and  this  one  is  located  accord- 
ing to  definite  laws.  If  the  two  receivers  are  pressed 
against  the  ears,  the  fused  sound  will  be  heard  at  the 
root  of  the  tongue — a  very  weird  experience.  The  laws 
.  for  the  localization  of  fused  sounds  are  among  the 
most  valuable  criteria  for  testing  a  theory  of  sound 
localization.^ 

To  revert,  then,  to  the  questions  at  the  beginning  of 
the  chapter,  we  may  sum  up  the  evidence  in  the  form  of 
a  reply.  The  following  points  may  be  considered  in 
favor  of  the  intensity  theory : 

(a)  The  general  variation  in  the  delicacy  of  localiza- 
tion ;  that  is,  the  form  and  distribution  of  the  sensory 
ellipses. 

(h)   The  existence  of  confusion-points. 

(c)  The  difficulty  of  localizing  sounds  radially  in  the 
median  plane. 

(d)  The  introspections  which  reveal  our  dependence 
upon  intensity. 

(e)The  inferiority  of  monaural  localization. 

From  experiments  of  this  kind  we  may  therefore 
conclude  that  intensity  is  tlie  primary  factor  in  the  local 
sign  of  hearing. 

But  intensity  operates  in  two  distinct  ways:  (1) 
through  the  binaural  ratio  and   (2)   through  monaural 

*  This  may  be  made  a  very  effective  demonstration  exercise  to 
be  developed  by  two  or  three  members  of  the  class. 


AUDITOEY  SPACE  69 

ratios.  With  two  ears  we  get  simultaneous  impressions 
in  which  the  intensity  for  one  ear  stands  in  a  certain 
ratio  to  the  intensity  for  the  other  ear.  But,  for  each 
ear  or  with  a  single  ear,  a  sound  in  one  direction  has  a 
certain  intensity  ratio  to  the  same  sound  in  another 
direction."^ 

We  have  also  found  distinct  evidence  of  another 
factor,  namely  tone  quality,  or  the  modification  of  the 
character  of  the  sound  by  the  form  of  the  outer  ear. 
Among  the  evidences  for  this  are : 

(a)  Complex  sounds  can  be  localized  more  accurately 
than  relatively  pure  tones. 

(h)  The  possibility  of  improvement  with  practice, 
especially  within  the  median  plane. 

(c)  The  inability  to  localize  pure  tones  by  one  ear 
alone. 

(d)  The  curve  of  monaural  localization. 

(e)  The  introspective  evidences;  i.e.,  consciousness 
of  quality  difference. 

Hence  we  shall  conclude  in  favor  of  the  fifth  theory, 
the  intensity-quality  theory :  sound  is  localized  by  means 


*  An  interesting  corroboration  of  this  twofold  nature  of  the 
local  sign  of  direction  of  sound  is  found  in  the  "teeth"  of  the 
curve  in  Fig.  10.  There  are  five  prominent  teeth,  namely,  15°  E,F, 
50°  RF,  90°  R,  60°  RB,  and  25°  RB.  The  more  accurate  the  meas- 
urement the  more  distinct  these  teeth  become.  Now,  the  explana- 
tion is  to  be  found  in  the  fact  that  there  is  a  change  at  these 
points  in  the  means  of  localization.  At  15°  RF  and  25°  RB  there 
is  a  transition  from  the  simple  balancing  of  the  relative  intensity 
of  the  two  ears  to  the  recognition  of  quality  changes  for  one 
ear.  At  50=  RF  and  00°  RB  there  is  a  transition  from  this  double 
standard  to  the  monaural  localization  on  the  basis  of  the  char- 
acter of  the  sound.  The  large  peak  at  90°  R  is  due  to  the  fact 
that  this  represents  a  sort  of  zero-point  for  both  modes  of  local- 
ization. 


VO  AUDITORY   SPACE 

of  binaural  and  monaural  ratios  of  intensity  and 
characteristic  differences  in  quality.  * 

Is  the  ear  a  space-sense  organ  'i  It  is.  As  we  have 
in  two  eyes  a  means  for  the  perception  of  distance,  we 
have  two  ears  for  the  perception  of  direction.  We  also 
have  on  each  side,  where  the  two  ears  cannot  well  co- 
operate, ear-funnels  which  change  the  quality  and  the 
intensity  of  the  sound  with  reference  to  the  direction  in 
which  the  vibrations  impinge  upon  one  ear. 

Movement,  tendencies  to  movement,  images  of 
movement,  visual  or  auditory  images,  tactual  sensations 
or  images,  and  other  factors  may  have  been  observed  as 
secondary  factors  which  influence  localization. 

What  are  some  of  the  laws  of  localization?  The 
graphic  representation  in  Fig.  11,  for  example,  embodies 
a  whole  system  of  laws.f 

*Quality  is  here  used  in  the  popular  sense,  as  synonymous 
with  timbre.     Strictly,  the  quality  of  the  tone  is  its  pitch. 

fA  good  survey  of  this  topic  is  found  in  Pierce,  ".Studies  in 
Space-perception.*'  The  present  chapter  is  based  mainly  upon 
Starch,  "The  Localization  of  Sound,"  The  University  of  Iowa 
Studies  in  Psychology,  Nos.  4  and  5. 


CHAPTER  VI 
TACTUAL  SPACE 

For  Two. 
1.  Tactual  Localization  of  a  Point. — Mark  off  an 

area  50  millimeters  wide  and  100  millimeters  long  from 
the  wrist  upward,  on  the  volar  (inner)  surface  of  the 
forearm  by  ink-dots  at  the  corners  of  the  parallelogram. 
Make  a  similar  plot  in  the  note-book.  Working  within 
this  area,  touch  O,  who  sits  with  eyes  closed,  lightly 
with  the  point  of  a  pencil  and  require  him  to  try  to 
locate  this  spot,  eyes  opened,  by  touching  with  another 
pencil.*  Mark  the  relative  positions  of  the  two  spots 
by  dots  in  the  note-book  plot,  and  connect  them  by  a 
light  line  to  indicate  the  magnitude  of  the  error.  Label 
the  dots  S  (stimulus)  and  L  (location)  respectively. 
Make  15  trials.  Kecord  O's  analysis  of  what  con- 
stitutes the  ''local  sign" — the  terms  in  which  he  recog- 
nizes the  location  of  a  touch.f 

There  are  three  factors  in  the  record:  the  measure- 
ment of  accuracy  of  localization  in  terms  of  the  magni- 
tude of  the  error;  the  direction  of  the  error;  and  the 
analysis  of  the  local  sign. 

Accuracy  of  localization  varies  for  different  parts  of 
the  skin ;  in  general,  the  portions  of  the  skin  which  are 

*  Keep  the  results  secret  from  O. 

f  For  definition  of  local  sign  see  Ch.  IV,  p.  45. 

71 


72  TACTUAL  SPACE 

used  most  in  tactual  perception  are  most  sensitive. 
Hence  we  find  but  a  crude  localization  for  the  large 
areas  for  which  tactual  localization  is  relatively  un- 
important, and  a  fine  ability  for  those  portions  which 
are  small,  movable,  and  readily  accessible.  This  should 
be  illustrated  in  the  chart  just  made  by  large  errors  in 
that  portion  which  is  toward  the  middle  of  the  forearm, 
and  small  errors  at  or  near  the  wrist. 

The  probable  direction  of  an  error  is  predictable  ac- 
cording to  a  general  law ;  the  point  touched  is  generally 
misplaced  toward  the  nearest  joint  or  actively  used  por- 
tion of  the  skin  in  the  localization.  This  should  show 
in  the  chart  by  a  tendency  of  the  L-dots  to  be  nearer  the 
wrist  than  the  S-dots.  The  largest  errors  are  along  the 
axis  of  the  arm,  unless  the  point  touched  is  on  or  very 
close  to  the  wrist.  The  errors  in  the  radial  and  ulnar 
directions  are  small. 

It  is  difficult  to  discover  by  introspection  just  what 
constitutes  the  local  sign.  The  localization  of  the 
tactual  impression,  like  the  projection  of  the  retinal 
image,  is  automatic.  The  mode  of  the  accompanying 
consciousness  varies  for  different  parts  of  the  skin  and 
with  different  individuals.  The  record  might  mention 
visual  imagery,  association  with  blood-vessels,  ridges, 
wrinkles,  curvatures,  relative  callousness  of  the  skin, 
tendencies  to  movement,  etc.  The  following  account  of 
the  local  sign  of  the  skin  is  apposite. 

"Not  only  is  the  skin,  pliysiolopfically  regarded,  a  localizing 
organ:  the  organism  is  endowed  with  reflex  localizing  movements, 
Tf  a  spot  of  the  skin  is  irritated,  hand  or  foot  moves  to  it  re- 
flexly,  in  obedience  to  purely  physiological  laws.  Out  of  this 
nnconseioiis  localization  the  conscious  local  mark  arises,  by  the 
following  stages:    (a)   The  movement  of  the  hand  or  foot,  though 


TACTUAL  SPACE  73 

reflexly  set  up,  occasions  organic  sensations  in  the  joint,  tendon, 
etc. ;  so  that  definite  groups  of  organic  sensations  become  con- 
nected with  pressures  upon  particular  parts  of  the  body.  The 
local  sign  may  consist,  therefore,  of  remembered  organic  sensa- 
tions. (6)  The  reflex  movement  toward  the  irritated  spot  will 
usually  be  seen;  so  that  the  local  sign  may  contain  a  visual  sen- 
sation, a  picture  of  the  part  touched,  as  well  as  organic  sensa- 
tions, (c)  The  organic  sensations  may  pass  unnoticed,  owing 
to  the  habitual  nature  of  the  movement.  The  local  sign  of  a 
pressure  will  then  be  a  sensation  of  a  quite  different  order — a 
sensation  of  sight.  (d)  Finally  the  visual  picture  itself  may 
disappear,  and  its  place  be  taken  by  a  word,  the  name  of  the 
part  of  the  body  pressed.  Often  enough,  when  we  say  that  we 
remember  an  occurrence,  we  remember  only  the  form  of  the 
word  which  describes  it.  So  now,  when  I  am  touched  upon  the 
arm,  there  flashes  up  in  my  mind  the  word  'arm,'  and  this  word 
is  the  local  sign  of  the  pressure." — Titchener,  "Outlines  of  Psychol- 
ogy," p.  157. 

Tactual  space  is  inseparably  bound  up  witb  visual 
space.  In  this  experiment  it  is  extremely  difficult  to 
make  a  purely  tactual  localization;  there  is  almost  in- 
variably at  least  a  visual  image  of  the  arm  and  particu- 
larly the  portion  stimulated.  To  test  the  effect  of  the 
visual  image  upon  the  accuracy  of  localization,  experi- 
ments have  been  made  upon  trained  observers  who  had 
the  power  of  practically  inliibiting  the  visual  images,  of 
neglecting  them,  or  of  utilizing  them  in  locating  the 
pressure  sensations.  The  results  show  much  greater 
accuracy  with  the  employment  of  visual  imagery  than 
without  it. 

Blind  persons,  however,  who  cannot  rely  upon  the 
visual  imagery,  exhibit  no  larger  errors  in  localization 
than  seeing  persons.  This  is  of  course  due  to  the  great 
reliance  wdiich  they  must  place  upon  pressure  sensa- 
tions, and  to  the  practice  effects  in  delicacy  of  discrimi- 
nation which  follow.  This  would  tend  to  show  that, 
although  vision  constitutes  for  normal  persons  an  im 


74  TACTUAL  SPACE 

portant  element  in  the  local  sign  of  pressure,  it  is  not 
an  indispensable  element. 

The  right  arm  and  hand  of  the  observer  have  been 
used  to  carry  the  pencil  in  locating  the  pressure  sensa- 
tions. This  has  added  a  whole  group  of  muscle  sensa- 
tions further  to  complicate  matters.  It  is  well  known 
that  distances  are  not  properly  judged  by  movements  of 
the  arm  and  hand  when  flexed,  as  required  in  touching 
a  part  of  the  other  arm.  Much  of  the  constant  mis- 
placement distally  has  been  found  to  be  due  to  this 
factor.  This  suggests  again  the  interconnection  between 
tactual  and  muscular  space.^ 

2.  The  Two-point  Space  Threshold. — To  measure 
the  threshold  of  space  discrimination  for  two  points 
upon  the  skin,  determine  the  minimum  distance  that 
two  spots  lying  in  the  longitudinal  axis  of  the  volar 
surface  of  the  forearm,  stimulated  simultaneously,  may 
be  separated  and  still  be  perceived  as  two. 

From  a  calling-card  cut  a  strip  15  millimeters  wide 
and  as  long  as  the  card ;  cut  this  diagonally.  Take  the 
two  triangular  '^points,"  and  improvise  a  pair  of  com- 
passes by  holding  these  between  the  thumb  and  first 
finger.  Set  the  points  at  the  desired  distance  by 
measuring  on  the  millimeter  scale.  Adopt  the  follow- 
ing scale  of  steps  in  separation:  1,  2,  3,  4,  7,  11,  16,  22, 

*  Other  methods  of  localizing  have  been  designed  to  eliminate 
some  of  these  complicating  factors:  (a)  hold  the  pencil  just 
over  the  point  stimulated,  but  do  not  touch  the  skin;  (6)  mark 
the  localization  upon  a  photograph  or  plaster-of-Paris  model  of 
the  arm;  (c)  describe  in  words  as  nearly  as  possible  the  loca- 
tion. These  methods  may  be  combined  and  other  methods  de- 
rived from  them. 


TACTUAL  SPACE  75 

29,  37,  and  46  millimeters.  Press  the  two  points  simul- 
taneously, gently  and  evenly,  for  about  1  second  and  re- 
quire O  to  report  whether  he  feels  one  or  two."^  Start 
with  the  smallest  step,  and  if  O  reports  "One"  try  the 
next  larger  step,  and  continue  thus  until  O  reports 
"Two."  With  this  step  give  successive  trials,  inter- 
spersing control  trials,t  until  O  makes  a  mistake  or  has 
perceived  the  two  points  correctly  ten  times  in  succes- 
sion. If  a  mistake  is  made,  take  next  higher  steps  in 
order  until  ten  successive  correct  judgments  are  given 
on  one  step.  Record  the  number  of  correct  judgments 
for  each  step  tried;  the  last  may  be  considered  the 
threshold  required  and  a  measure  of  O's  power  of  space 
discrimination  under  these  conditions. 

3.  Relation  to  Direction  on  Limbs. — Measure,  in  a 
similar  manner,  the  two-point  space  discrimination  with 
the  compass-points  applied  in  a  transverse  direction  on 
the  same  region  as  in  Exp.  2.  Compare  results  with 
those  of  Exp.  2. 

4.  Relation  to  Part  of  Body. — Measure  the  two-point 
'space  discrimination,  as  in  Exp.  2,  (1)  on  the  tip  of  the 
first  finger  of  the  left  hand  and  (2)  in  a  vertical  line  on 
the  back  of  the  neck.     Record  and  compare  results. 

*  Avoid  all  unnecessary  fatigue  of  the  skin  area  selected  for  ex- 
ploitation. Take  great  care  to  apply  and  to  withdraw  the  two 
points  simultaneously.  Do  not  press  hard;  a  clearly  defined 
sensation  of  contact  is  all  that  is  necessary. 

t  Control  trials  may  be  made  by  touching  with  one  point  only 
in  about  one-third  of  the  trials;  if  O  answers  "Two"  in  a  control 
trial,  this  is  an  error  indicating  that  he  has  not  set  himself  a 
sufficiently  high  standard  of  certainty  and  he  must  be  tried  on 
a  next  higher  step. 


16  TACTUAL  SPACE 

The  two-point  space  threshold,  which  is  measured  in 
Exps.  2,  3,  and  4,  is  an  index  to  spatial  sensitiveness. 

Exp.  2,  the  results  of  which  may  seem  startling  to 
the  uninitiated,  demonstrates  the  fact  that  the  two 
points  may  be  separated  some  distance  and  yet  be  per- 
ceived as  one.  This  is  to  be  explained  upon  the  assump- 
tion that  the  local  signs  for  the  two  points  stimulated 
are  indistinguishable  and  therefore  there  is  no  basis 
for  a  differentiation  of  the  impressions.  The  two-point 
threshold  for  this  direction  upon  the  arm  is  large. 

In  Exp.  3,  with  a  transverse  direction  upon  the  arm, 
the  threshold  is  smaller.  This  is  in  line  with  the  fact, 
found  in  Exp.  1,  that  the  radial  and  ulnar  misplace- 
ments in  localization  are  small.  The  explanation  for 
this  is  based  in  part  upon  the  anatomical  fact  that  the 
pressure-spots  lie  closer  together  transversely  than  in  a 
longitudinal  direction. 

In  Exp.  4  the  spatial  sensitiveness  is  found  to  vary 
with  the  different  parts  of  the  body ;  upon  the  fingers  it 
is  very  delicate,  upon  the  neck  very  obtuse.  The  fol- 
lowing table  ^  gives  a  list  of  representative  threshold 
values  for  various  parts  of  the  body  in  longitudinal 
direction : 

Tongue-tip 1.1  m.m. 

Palm  side  of  last  phalanx  of  finger   2.2  " 

Red  part  of  lips   4.4  " 

Tip  of  nose    6.6  '' 

Back  of  second  phalanx  of  finger 11.0  " 

Heel    22.0  " 

Back  of  hand    30.8  " 

Forearm    39.6 

Sternum    44.0  " 

Back  of  neck    52.8  " 

Middle   of   back    66.0  " 

*  James,  Psychology,  Briefer  Course,  p.  62. 


TACTUAL  SPACE  11 

The  space  discrimination  in  any  given  portion  of  the 
skin  may  be  represented  by  so-called  sensory  circles, 
more  properly  called  sensory  ellipses,  on  the  same  plan 
as  we  represented  auditory  space  discrimination  in 
Chapter  V,  Fig.  11.  Thns,  the  data  in  this  table  would 
furnish  the  major  axes  for  ellipses. 

The  difference  in  distribution  of  the  pressure  end- 
organs  and  nerves,  the  unequal  amount  of  practice  oc- 
casioned by  exposure  and  use  of  certain  parts  of  the 
body,  and  habitual  protection  of  others  by  the  garments, 
are  probably  sufficient  to  account  for  the  wide  range  of 
the  two-point  threshold  on  different  bodily  regions. 

There  is  a  gTadual  transition  from  oneness  to  twoness. 
Titchener  quotes  from  Henri  the  following  introspec- 
tions for  a  series  of  increasing  distances: 

1.  One  small  sharp  point. 

2.  A  larger  blunter  point. 

3.  A  small  area  of  oval  form. 

4.  A  line. 

5.  Two  points,  near  together,  connected  by  a  line  of  light  contact. 

6.  Two  separate  points;   direction  of  line  of  junction  uncertain. 

7.  Two  separate  points;   direction  kno\Mi. 

The  two-point  space  threshold  varies  also  under  other 
conditions.  Practice  reduces  it ;  for  instance,  a  thresh- 
old of  14  millimeters  may  after  a  few  periods  of  prac- 
tice be  reduced  to  5  or  6  millimeters.  Practice  on  one 
area  also  lowers  the  threshold  for  other  bodily*  areas ; 
the  left  forearm  has  been  stimulated  and  the  threshold 
for  the  right  forearm  thereby  reduced  from  11  to  7 
millimeters  in  six  practice  periods.  On  the  other  hand, 
fatigue  raises  the  threshold;  that  is,  it  decreases  the 
sensitiveness.  And  drugs,  such  as  atropine,  morphine, 
strychnine,  and  alcohol,  have  a  similar  effect.     With 


78  TACTUAL  SPACE 

reference  to  temperature  it  may  be  said  that  if  the 
points  are  cold  when  they  are  applied  to  the  skin  the 
threshold  is  in  general  lower  than  if  the  stimulus  points 
are  warm :  the  cold  points  seem  to  be  more  sharply 
localized.  Warming  the  skin  before  applying  the 
points  also  increases  the  sensitiveness,  while  cooling  the 
skin  has  an  opposite  effect.  In  the  experiments  it  is 
best  to  exclude  simultaneous  temperature  sensations. 
Rotation  of  one  point  reduces  the  threshold.  Disease, 
especially  of  the  nervous  system,  affects  spatial  sensi- 
tiveness, sometimes  increasing,  sometimes  decreasing  it, 
depending  upon  the  nature  of  the  disturbance.  In  some 
diseases  all  pressure  sensations  are  lost  throughout  more 
or  less  circumscribed  skin  areas.  Very  large  individual 
differences  are  found  among  different  persons,  some 
being  several  times  more  sensitive  than  others. 

5.  Simultaneous  Compared  with  Successive  Touch. 
— Measure  the  two-point  space  discrimination  in  the 
same  region  and  in  the  same  manner  as  in  Exp.  2,  except 
that  instead  of  touching  the  two  spots  simultaneously 
you  touch  each  with  the  same  point  quickly  in  succes- 
sion. To  regulate  the  distance,  hold  a  ruler  near  the 
skin  as  a  guide. 

When  two  points  are  applied  successively  instead  of 
simultaneously,  as  in  Exp.  5,  the  threshold  for  the  dis- 
crimination of  two  points  is  very  much  lowered,  prob- 
ably by  about  one  half. 

Two  points  may  be  clearly  perceptible  as  two,  without 
knowledge  on  the  part  of  the  observer  of  the  direction 
of  one  from  the  other.     Two  successive  stimuli  were 


TACTUAL  SPACE  79 

correctly  perceived  as  two  upon  the  forearm  when  3 
millimeters  apart,  but  their  directions  were  known  only 
wdien  the  separation  was  increased  to  7  millimeters. 
These  figures  show  that  the  direction  threshold  is  larger 
than  the  difference  or  two-point  threshold.  The  same 
is  true  for  simultaneous  pressures.  An  analogous 
tendency  is  also  common  in  other  sensations;  for  in- 
stance, we  can  tell  that  an  odor  is  present  before  we 
can  identify  it,  or,  we  may  know  that  two  tones  are 
unlike  in  pitch  without  being  able  to  tell  which  is  the 
higher  one. 

Kelated  to  the  comparison  of  simultaneous  and  suc- 
cessive touch  is  the  discrimination  for  the  motion  of  a 
point  upon  the  skin.  We  can  detect  motion  before  we 
can  detect  the  direction  of  the  motion.  The  discrimina- 
tion for  motion  varies  greatly  with  the  rate  of  motion. 

6.  Method  "with  Knowledge"  Compared  with 
Method  "without  Knowledge." — Kepeat  Exp.  2,  but 
let  O,  with  his  eyes  open,  apply  the  compasses.  Eecord 
as  before. 

In  this  experiment  we  have  the  cooperative  effect  of 
the  visual,  tactual,  and  muscular  space  senses;  the 
method  is  ^Svith  knowledge"  as  compared  with  the 
method  of  Exp.  2,  which  was  "procedure  without  knowl- 
edge." The  two-point  threshold  by  this  method  is 
lower  than  when  obtained  by  the  method  'Svithout 
knowledge." 

The  most  effective  method  of  securing  a  knowledge 
of  objects  by  tactual  impressions  is  not  to  allow  them  to 
press  against  the  unmoved  skin,  but  to  pass  the  sensitive 
skin  surface  over  the  objects  and  thereby  gain  a  wealth 


80  TACTUAL  SPACE 

of  information  quite  impossible  by  the  passive  method. 
This  is  active  pressure.  It  is  keen,  quick,  and  sure. 
It  is  the  method  we  most  often  employ.  We  do  not 
test  the  smoothness  of  a  surface  by  simply  laying  the 
hands  upon  it;  we  rub  the  tips  of  the  fingers  upon  it. 
The  knife-grinder  draws  the  edge  of  the  blade  he  is 
sharpening  along  the  finger ;  he  does  not  merely  hold  the 
edge  of  it  against  the  finger.  In  active  pressure  the 
skin  really  seems  to  be  more  sensitive ;  certainly  the 
efficiency  of  the  sensitive  skin  in  mediating  sensations 
of  the  space  qualities  of  objects  is  very  much  increased, 
but  this  is  really  due  to  favorable  conditions  for  percep- 
tion and  does  not  indicate  any  real  increase  in  sensitive- 
ness after  all. 

The  blind  live  in  a  world  of  tactual,  muscular,  and 
auditory  space.  Their  fine  space  distinctions  are  made 
by  touch,  in  which  they  acquire  most  extraordinary 
skill.  A  blind  person  can  read  with  his  finger-tips 
almost  as  fast  as  we  ordinarily  read  with  our  eyes, 
impossible  though  it  may  seem.  The  print  for  the 
blind  consists  in  raised  points  or  ridges  made  by  em- 
bossing a  stiff  paper.  We  experience  difficulty  in  de- 
tecting even  the  form  of  a  single  letter  by  touch.* 

Yet  the  superiority  of  the  blind  in  this  capacity  does 
not  lie  so  much  in  superior  sensitivity  as  in  the  habit  of 
couching  impressions  in  tactual  terms.  The  two-point 
threshold  is  only  a  trifle  lower  in  the  blind  than  in  see- 

*  The  style  of  the  raised  print  has  been  improved  by  experi- 
ments on  the  principles  here  studied;  for  example,  on  the  rela- 
tive legibility  of  a  line  as  compared  with  a  dot  alphabet,  or  sim- 
ultaneous impressions  of  dots  compared  with  successive  impres- 
sions, most  favorable  spacing,  etc. 


TACTUAL  SPACE  81 

ing  persons  after  brief  practice ;  and  the  blind  person's 
sensitivity  to  pressure  does  not  differ  much  from  that 
of  seeing  persons  under  careful  experimental  condi- 
tions,"^ But  the  blind  person  is  a  "tadile.^^  He  thinks 
in  terms  of  touch  as  we  think  in  terms  of  sight.  Tac- 
tual discriminations  therefore  have  immediate  meaning 
to  him.  The  superiority  of  the  blind  in  this  activity 
is  not  in  sensation  but  in  perception.  This  is  a  funda- 
mental but  neglected  distinction. 

When  we  read  we  see  one  word  at  a  time  by  direct 
vision,  and  the  words  around  this  shade  off  gradually  in 
indirect  vision.  In  the  same  manner  the  blind  person 
gets  a  clear  image  of  one  letter  or  word  at  a  time  by  the 
left  hand  and  skirmishes  with  the  right  so  as  to  get  a 
general  impression  of  what  lies  ahead.  He  may  also 
learn  to  read  by  word  instead  of  letter  units. 

*  Put  a  human  hair  3  centimeters  long  on  a  sheet  of  smooth 
glass.  Lay  over  it  a  sheet  of  clear  writing-paper  and  locate  the 
hair  by  touch.  Add  sheet  after  sheet  and  locate  as  before  until 
you  come  to  such  thickness  that  you  cannot  locate  the  hair  by 
touch.  The  greatest  thickness  through  Avhich  the  hair  can  be 
located  correctly  is  a  measure  of  the  sensitivity  to  pressure.  The 
average  person  whose  hands  are  not  callous  should  locate  the  hair 
under  forty  to  fifty  sheets  of  "20-pound"  bond  paper.  A  blind 
person  cannot  do  very  much  better. 


CHAPTEE  VII 
CUTANEOUS  SENSATIONS 

For  One* 
The  problem  is  to  explore,  identify,  and  plot  charts 
of  cold  spots,  warmth  spots,  pain  spots,  and  pressure 
spots  found  in  the  skin. 

Outline  four  blocks,  each  10  by  10  millimeters,  into  2- 
millimeter  squares  with  pen  and  ink  on  the  back  of  the 
left  hand.  Outline  a  copy  of  each  of  these  in  the  note- 
book and  label  them  Cold,  Warmth,  Pain,  and  Pressure 
respectively,  t 

Put  six  of  the  nails  on  crushed  ice  and  the  other  six 
into  water  just  below  the  boiling-point. t  The  sense- 
organs  in  the  skin  fatigue  very  quickly — almost  in- 
stantaneously— when  touched.  Therefore,  select  points 
for  stimulation  systematically;  follow  parallel  lines, 
apply  the  stimulus  with  precision  and  with  a  constant 
vertical  pressure,  remove  it  within  a  second,  and  always 
trust  to  first  impressions.  Make  a  few  preliminary 
trials  for  practice  on  some  other  skin  area. 

*  Provide  a  dozen  tenpenny  wire  nails,  a  small  cork,  a  horse- 
hair from  the  mane,  warm  water,  and  ice. 

•j-  Freehand  ruling  is  accurate  enough  for  the  purpose. 

I  For  more  accurate  work  a  pointed  metal  tube  is  kept  at  a 
constant  temperature  by  having  warm  or  cold  water  at  the  de- 
sired temperature  How  through  it.  Another  way  is  to  put  the 
warm  water  or  crushed  ice  into  a  tube  and  change  it  as  often  as 
necessary. 


CUTANEOUS  SENSATIONS  83 

1.  Cold  Spots. — With  the  point  of  a  cold  nail,  explore 
a  plotted  area  of  the  skin  systematically  and  mark  on 
the  note-book  copy  of  this  plot  the  location  and  approxi- 
mate area  of  the  spots  which  give  rise  to  clear  and 
localized  sensations  of  cold.* 

When  the  cold  nail  touched  certain  portions  of  the 
skin  it  did  not  feel  cold ;  but  at  other  places  definite  and 
nmnistakable  sensations  of  cold  were  experienced. 
These  spots  may  perhaps  be  spoken  of  more  properly 
as  areas. 

2.  Warmth  Spots. — Take  a  warm  nail — as  warm  as 
it  can  be  made  without  making  it  uncomfortable  to  hold 
in  the  hand — and  survey  another  plotted  area  system- 
atically, and  mark  on  its  copy  the  location  and  approx- 
imate area  of  the  spots  which  give  rise  to  clear  and 
localized  sensations  of  warmth. 

The  spots  sensitive  to  warmth  are  more  difficult  to 
find.  The  warmth  spots  are  less  numerous  than  the 
cold,  they  are  less  sharply  localized,  and  they  seem  to 
lie  deeper  do^^ai  in  the  skin  than  the  cold  spots.  The 
warmth  sensations  do  not  follow  so  quickly  after  the 
application  of  the  stimulus  as  do  the  cold  sensations; 
that  is,  there  is  a  more  appreciable  latent  time.  The 
area  of  a  warmth  spot  usually  seems  larger  than  that  of 
a  cold  spot. 

The  kind  of  stimulus  which  can  best  call  forth   a 

*  Start  at  one  side  and  pass  by  parallel  lines  until  the  whole 
plot  has  been  covered  by  point  stimulations.  Never  retrace  or 
verify  in  the  same  sitting.  Lift  the  nail  vertically  up  and  down 
and  touch  with  the  very  point.  Change  the  nails  as  often  as  it 
is  necessary  to  keep  them  cold.  If  the  spots  are  large  and  taper 
off,  this  may  be  shown  by  shading  on  the  chart. 


84  CUTANEOUS  SENSATIONS 

certain  sensation  is  known  as  an  adequate  stimulus. 
Thus,  light-waves  constitute  the  adequate  stimulus  for 
sight  sensations.  The  adequate  stimulus  for  sensations 
of  cold  is  the  cooling  of  the  skin,  or  the  lowering  of  its 
temperature ;  that  for  w^armth  is  the  warming  of  the 
skin,  or  the  raising  of  its  temperature,  in  other  words 
the  application  of  radiant  energy. 

NTow,  since  the  skin  is  not  the  same  temperature  all 
over  the  body,  the  same  object  may  feel  warm  to  one 
part  and  cool  to  another.  The  temperature  of  a  given 
portion  of  the  skin  at  a  given  time  is  known  as  its 
physiological  zero-point.  Whether  or  not  the  stimulus 
shall  excite  the  cold  or  w^armth  spots  depends  in  part 
upon  the  physiological  zero-point;  if  the  stimulus  is 
slightly  warmer  than  the  skin,  w^armth  sensations  re- 
sult ;  if  it  is  slightly  cooler,  cold  sensations  result. 

The  nerve-endings  in  the  skin  which  correspond  to 
the  cold  spots  are  probably  separate  and  distinct  from 
those  which  correspond  to  the  warmth  spots.  Each 
temperature  spot  has  its  own  nerve-fiber  or  group  of 
fibers  which  responds  with  its  own  characteristic  sensa- 
tion only ;  that  is,  it  has  its  own  specific  energy.  This 
means  that  even  though  a  warm  stimulus  be  applied 
to  a  cold  spot,  a  sensation  of  cold  and  that  only,  if  any, 
will  result.  The  same  principle  applies  to  warmth 
spots.  Ordinarily  only  warmth  spots  respond  to  a  warm 
stimulus  and  cold  spots  to  a  cold  stimulus,  but  they 
sometimes  respond  to  inadequate  stimuli,  so  that  a 
neutral  stimulus,  say  a  pin,  may  be  used  to  find  all  four 
kinds  of  spots  called  for  in  this  chapter. 

Cold  and  warmth  are  the  two  qualities  of  temperature 


CUTANEOUS  SENSATIONS  85 

sensations.  Introspection  has  revealed  a  third  tem- 
perature experience  qualitatively  different  from  cold 
and  warmth,  the  perception  heat.  Heat  or  hotness  is 
something  distinct  from  mere  warmth,  and  it  is  not  due 
alone  to  the  excessive  stimulation  of  a  warmth  nerve. 
Heat  is  due  to  a  fusion  of  cold  and  warmth  sensations 
aroused  by  the  simultaneous  stimulation  of  cold  and 
warmth  nerves  by  rather  high  temperatures.  That  is, 
the  same  stimulus,  by  radiation  of  heat  or  otherwise, 
excites  both  cold  and  warmth  nerves,  each  of  which 
responds  with  its  specific  sensation,  but  the  complex 
experience  is  neither  that  of  cold  nor  of  warmth  but  of 
heat. 

The  fact  of  temperature  spots  was  discovered  inde- 
pendently by  Blix,  Goldscheider,  and  Donaldson  in  the 
years  1884  and  1885.  It  is  thought  that  the  nerve- 
endings  of  Ruffini  are  the  organs  for  warmth,  and  the 
endings  of  Krause  are  the  organs  for  cold.* 

3.  Pain  Spots. — Slit  the  small  end  of  the  cork  and 
insert  a  horsehair  into  the  slit,  so  that  a  squarely  cut 
end  of  the  hair  projects  from  one  side  about  5  milli- 
meters, f  Hold  the  cork  firmly  near  the  slitted  end, 
and,  by  pressing  the  hair  down  vertically  until  it  begins 
to  bend,  survey  a  third  plotted  area  systematically  and 
mark  on  the  copy  of  it  the  location  of  those  spots  which 
give  rise  to  clear  and  localized  sensations  of  pain. 

*  See  Barker,  "The  Nervous  System." 

f  The  bristle  should  project  from  the  cork  about  3  millimeters 
if  the  hand  is  callous,  or  10  millimeters  if  it  is  very  sensitive. 
Adjust  the  length  of  the  hair  between  these  two  limits  as  re- 
quired.    The  pressure  exerted  should  be  as  uniform  as  possible. 


8G  CUTANEOUS  SENSATIONS 

When  the  whole  plot  has  been  surveyed,  verify  about 
a  dozen  pain  spots  by  a  single  touch  at  each  and  mark 
differences  in  intensity  of  painfulness  on  the  scale  of 
1,  2,  3,  where  1  represents  the  faintest  and  3  the 
strongest  sensations,  by  connecting  each  spot  with 
a  number  in  the  margin,  as  in  correcting  printer's 
proof. 

Pain  spots  are  easily  located,  and  the  pain  sensations 
are  very  vivid  and  very  unlike  any  other  cutaneous 
sensations.  The  pain  sensations  usually  give  rise  to 
distinct  reflex  movements;  indeed  the  movement  is 
sometimes  perceived  before  the  pain.  The  pain  spots 
are  more  numerous  than  even  the  cold  spots ;  and,  while 
they  themselves  are  very  sensitive,  intervening  skin 
areas  are  usually  quite  angestl^^c  as  regards  pain,  some- 
times to  such  a  degree  tha^^fceedle  may  be  inserted 
deeply  into  the  skin  wdthoi^»ain.  The  cold  and 
warmth  spots  are  analgesic,  i.^Misensitive  to  pain ;  but 
it  is  difficult  to  stimulate  thes^Rhout  at  the  same  time 
stimulating  one  of  the  very  numerous  pain  spots.  Pain 
spots  are  to  be  found  only  upon  the  skin  or  structures 
closely  connected  with  it  genetically.  The  free  nerve- 
endings  in  the  skin  are  probably  the  end-organs  of 
pain.  t 

There  is  no  single  adequate  stimulus  for  pain.  Any 
of  the  general  classes  of  stimuli — mechanical,  thermal, 
chemical,  electrical — will  cause  pain.  This  general 
nature  of  pain  stimuli  is  necessary  from  the  biological 
point  of  view.  Pain  is  one  of  the  most  valuable  en- 
dowments of  living  organisms  in  enabling  them  to  avoid 
danger.     Pain  means  disaster ;  when  an  experience  be- 


CUTANEOUS  SENSATIONS  87 

comes  painful  it  means  that  injury  may  follow  unless 
there  is  some  protective  reaction.  The  point  at  which 
experiences  become  painful  is  usually  just  before  injury 
is  likely  to  result.  From  the  point  of  view  of  evolution, 
pain  was  probably  the  first  experience  to  appear,  be- 
cause the  most  necessary.  It  is  still  the  best  safeguard 
we  ourselves  have  against  bodily  injury. 

That  pain  is  a  special  sense  is  a  relatively  recent  dis- 
covery. It  was  formerly  thought  that  pain  resulted 
from  the  excessive  stimulation  of  any  sensory  nerve. 
Such,  however,  is  not  the  case.  The  pain  we  experience 
under  the  influence  of  a  very  bright  light  comes  from 
real  pain-nerves  in  the  eye,  not  from  the  overstimula- 
tion of  the  optic  nerve.  The  most  bitter  sen- 
sations are  not,  in  the  fl|pt  sense  of  the  word,  pain- 
ful. AVhen  we  bear  in  hiind  the  profuse  distribu- 
tion of  the  pain  end-brgans  and  the  general  nature 
of  pain  stimuli,  the  above  fact  readily  becomes  intel- 
ligible. 

Our  English  word  ''pain''  is  ambiguous.  We  use  it  to 
refer,  on  the  one  hand,  to  pain  sensations,  as  in  this 
chapter ;  and,  on  the  other  hand,  to  refer  to  the  feeling 
of  unpleasantness."^  Now,  pain  sensations  are  nearly 
always  unpleasant,  but  not  all  unpleasant  experiences 
are  painful  by  any  means.  It  is  exceedingly  unpleasant 
to  overturn  one's  cup  of  coffee  at  dinner,  but  it  is  not 
necessarily  painful  unless  one  happens  to  be  scalded  by 
the  liquid.     As  we  have  used  the  word  pain,  it  has  had 


*  The  Germans  have  two  words,  "Schmerz"  and  "Unlust",  to 
cover  the  ground  of  our  word  pain. 


88  CUTANEOUS  SENSATIONS 

reference  alone  to  a  special  sense  of  pain,  with  central, 
peripheral,  and  connecting  nervous  apparatus  such  as 
every  other  special  sense  possesses. 

Pain  sensations  have  only  one  quality,  pain.  The 
various  kinds  of  pain'  we  think  we  exj^erience,  such  as 
throbbing,  burning,  sharp  or  dull  pains,  are  due  to 
variation  in  attributes  other  than  quality  and  to  the 
accompaniment  of  sensations  other  than  pain.  Thus,  a 
prick,  a  pinch,  a  toothache,  and  a  headache  differ  in  local 
sign,  areal  distribution,  intensity,  duration,  and  com- 
bination with  other  sensations,  but,  as  pains,  they  all 
have  the  same  quality. 

4.  Pressure  Spots. — With  the  same  finder  as  in  Exp. 
3,  and  in  the  same  manner,  survey  the  plotted  area  and 
mark  on  the  copy  of  it  the  spots  which  give  rise  to  clear 
and  localized  sensations  of  pressure.  Record  on  the 
same  plot  the  relative  position  of  the  nearest  hair  to 
each  pressure  spot. 

.  The  fourth  specific  cutaneous  sensation  is  pressure. 
Pressure  spots  are  more  numerous  than  cold  and 
warmth  spots,  but  less  numerous  than  pain  spots.  They 
are  distributed  over  the  surface  of  the  whole  body  and 
extend  some  distance  into  the  natural  openings  of  the 
body  cavities.  Each  minute  hair  on  the  body  has  its 
pressure  spot,  usually  situated  to  the  windward, 
but  pressure  spots  also  occur  on  the  hairless 
regions.  The  pressure  nerves,  which  of  course  are 
distinct  from  the  temperature  and  pain  nerves,  have  a 
specialized  mode  of  termination  in  the  skin,  each  nerve- 
fiber  bearing  a  little  terminal  bulb,  such  as  the  Pacinian 


CUTANEOUS  SENSATIONS  89 

corpuscle  or  the  spindle  of  Meissner.     The   adequate 
stimulus  for  pressure  is  mechanical. 

Pressure  sensations  are  of  one  quality  only,  usually 
described  as  feeling  like  a  tiny  seed  embedded  in  the 
skin  and  pressed  downward.  Ordinarily  this  peculiar 
quality  is  not  noticed,  as  a  number  of  pressure  spots 
are  stimulated  simultaneously,  and,  for  the  most  part, 
there  are  accompanying  temperature  and  pain  sen- 
sations. 

In  all  the  above  cutaneous  sensations  we  assume  that 
the  ^'spot"  of  a  specific  character  is  due  to  the  presence 
of  the  corresponding  specific  end-organ.  The  spot  be- 
comes an  appreciable  area  when  the  taut  skin  sur- 
rounding the  end-organ  communicates  the  stimulus 
indirectly. 

A  few  years  ago  a  schoolboy  who  did  not  know  how 
many  senses  he  had  would  have  been  considered  a  dull 
boy.  He  learned  on  his  father's  knee  that  he  had  five, 
the  five  gates  to  Milton's  city  of  Man-soul,  namely,  eye- 
gate,  ear-gate,  nose-gate,  tongue-gate,  and  feel-gate. 
To-day  the  professor  of  psychology  does  not  know  with 
certainty  how  many  senses  he  has,  but  he  does  know 
that  he  has  more  than  five — possibly  twice  as  many  as 
he  was  supposed  to  have  fifty  years  ago.  The  newer 
senses  have  been  discovered  and  explored  by  the 
natural-history  method  followed  in  these  experiments. 

How  shall  we  know  when  we  come  across  a  new 
sense  ?  Among  the  chief  criteria  are  the  following :  (1) 
the  sensation,  as  a  conscious  experience,  is  unlike  every 
other  know^n  sense  quality;  (2)  it  is  objective  and 
localized,  and  (3)   it  comes  through  specific  end-organs. 


90  CUTANEOUS  SENSATIONS 

Some  psychologists  and  physiologists  hold  that  hunger 
and  thirst  are  special  senses,  but  the  prevailing  opinion 
is  that  hunger  and  thirst  fail  on  the  first  and  the  third 
criteria;  they  can  be  reduced  to  other  known  sense- 
complexes. 


CHAPTER  Vin 

WEBEK'S  LAW 

For  Two.* 

If  you  can  just  barely  perceive  a  difference  of  one 
gram  added  to  twenty  grams,  what  is  the  smallest  dif- 
ference you  can  perceive  when  added  to  forty  grams  1 
Eighty  grams  ?     Two  hundred  grams  ? 

Weber's  law  gives  the  answer:  ^ 'Equal  difference 
between  sensations  means  proportional  difference  be- 
tween stimuli."  The  ratio  just  posited  is  1 :20 ;  hence 
2  grams  added  to  40  grams,  4  grams  added  to  80  grams, 
and  10  grams  added  to  200  grams  would  be  equally  per- 
ceptible. 

This  law  applies  in  various  ways  in  the  different 
senses.  Weber  first  demonstrated  it  for  the  perception 
of  w^eight,  and  as  this  field  presents  the  simplest  as  well 
as  the  most  exact  conditions  for  measurement,  we  shall 
verify  and  illustrate  the  law  for  lifted  weights. 

Specifically,  this  is  what  w^e  shall  try  to  do:  Exp.  1 
is  a  preliminary  skirmish  to  determine  within  what 
range  of  weight  it  wdll  be  most  profitable  to  make  the 
measurement  on  the  observer ;  Exp.  2  reduces  this  to  an 
exact  measurement;  and  Exp.  3  makes  the  same 
measurement  with  doubled  weight  and  doubled  incre- 

*  Provide  two  tumblers,  some  medium-sized  shot  or  small  nails 
or  coins,  a  wad  of  cotton,  and  two  small  pieces  of  woolen  cloth. 

91 


92  WEBER'S  LAW 

ment.  Now,  if  Weber's  law  holds,  there  should  be 
about  the  same  degree  of  success  in  the  discrimination 
in  Exps.  2  and  3. 

Select  two  ordinary  tumblers  of  the  same  kind  and 
weight.  A  fairly  heavy  jelly-glass  is  good,  but  the  sides 
must  slope  so  that  the  one  fits  snugly  into  the  other. 
Put  a  wad  of  cotton  or  soft  cloth  into  the  bottom  of  one. 
Make  a  cushion  out  of  three  or  four  folds  of  cloth  on 
which  to  set  the  glass. 

Prepare  a  differential  weight  as  follows:  Take  a 
quantity  of  small  pieces  of  metal  that  are  uniform  in 
weight  (e.g.,  small  coins,  nails,  or  shot)  and  select  Avhat 
you  judge  to  be  about  one  tenth  the  weight  of  a  glass. 
Tie  these  into  a  small  cloth  so  that  this  bag  can  be  lifted 
into  the  glass  and  out  of  it  quickly  and  without  sound 
or  other  disturbance. 

Blindfold  O  and  let  him  be  seated  at  the  table  with 
the  padded  glass  before  him  in  such  a  position  that  he 
can  lift  it  conveniently  and  accurately  by  a  free-arm 
movement.  Vary  the  weight  of  the  glass  by  putting  the 
differential  weight  into  it  or  taking  it  out  for  successive 
trials.  Every  precaution  must  be  taken  to  prevent  any 
other  means  of  information  than  the  actual  sense  of 
weight.  Use  two  signals :  ''Keady"  for  the  first  of  two 
liftings  in  a  comparison,  and  ''Now"  for  the  second. 
Make  the  time  between  the  two  liftings  as  short  as 
possible.  Allow  repetition  of  a  trial  only  when  the 
observer  calls  for  it  on  the  ground  of  some  specific  dis- 
turbance. Any  accidental  clue  obtained  from  the  ex- 
perimenter would,  of  course,  be  such  disturbance. 

To  determine  the  order  in  a  comparison,  flip  a  coin 


WEBER'S  LAW  93 

for  each  trial  and  put  the  differential  weight  into  the 
first  lifting  if  head  is  up,  or  into  the  second  if  tail  is  up. 

1.  The  Approximate  Threshold  of  Discrimination 
for  Weight. — Let  O  lift  the  glass  twice  in  close  succes- 
sion and  say  whether  it  was  heavier  in  the  first  or  the 
second  lifting.  If  O  is  right  in  more  than  75  per  cent 
of  a  few  trials,  lessen  the  differential  weight ;  if  he  is 
right  only  in  much  less  than  75  per  cent  of  the  trials, 
increase  it.  Skirmish  in  this  way  until  you  get  such  an 
increment  of  the  weight  that  O  will  get  ahout  75  per 
cent  of  the  judgments  right  in  20  trials.  Between  65 
and  85  per  cent  will  do.  The  increment  thus  obtained 
is  the  one  with  which  to  make  the  more  accurate 
measurement  in  the  next  experiment.  Record  it  in 
terms  of  the  number  of  objects  (coins,  nails,  or  shot). 

The  weight  of  an  object  is  judged  most  accurately 
when  it  is  lifted  in  the  most  convenient  position.  The 
same  object  appears  to  be  heavier  if  gTasped  lightly  than 
if  grasped  tightly.  An  object  appears  heavier  if  lifted  v 
in  contact  with  a  small  area  of  skin  than  if  in  contact 
with  a  larger  area.  An  object  appears  heavier  if  lifted 
with  a  slow  movement  than  if  lifted  by  a  quick,  but  not 
jerking,  movement.  A  heavy  weight  grows  heavier  and 
a  light  weight  grows  lighter  when  sustained  undisturbed 
in  the  hand.  Of  two  equal  weights  lifted  in  succession, 
the  second  appears  to  be  the  heavier.  An  object  of 
moderate  weight  appears  to  be  heavier  or  lighter  than  it 
really  is  according  as  a  lighter  or  a  heavier  object  has 
been  lifted  just  before.  An  object  held  in  one  hand 
appears  to  be  lighter  than  it  really  is  if  the  other  hand 


94  WEBER'S  LAW 

supports  another  weight  or  is  otherwise  engaged,  as  in 
a  gi'ip  or  push.  Any  deviation  from  the  physiological 
zero  of  temperature  increases  the  apparent  weight  of 
the  object.  An  object  appears  to  be  heavier  or  lighter 
than  it  really  is  according  as  the  material  of  which  it  is 
made  suggests  lighter  or  heavier  weight  than  the  actual. 
Of  two  objects  that  are  of  the  same  weight  but  different 
size,  the  larger  appears  to  be  the  lighter  when  lifted. 

This  formidable  array  of  assertions  represents  some  of 
the  well-established  laws  of  the  perception  of  Aveight. 
These  laws  must  be  kept  clearly  in  mind  in  the  per- 
formance of  a  weight  test  in  order  to  avoid  introducing 
errors  which  would  result  from  the  violation  of  such 
laws.  Thus,  two  objects  which  are  to  be  compared  in 
weight  by  lifting  must  be  lifted  in  the  same  position; 
they  must  be  gTasped  with  the  same  area  of  pressure, 
and  A\dth  a  grip  j^roportional  to  their  weights ;  they  must 
be  lifted  at  the  same  rate,  to  the  same  height,  and  be 
sustained  the  same  length  of  time;  the  order  must  be 
alternated  fairly;  contrast-weight,  counter-weight,  or 
division  of  energy  must  be  avoided;  temperature  must 
be  kept  constant ;  the  weights  must  appear  to  be  made 
of  the  same  material  and  must  be  of  the  same  size. 
Violation  of  these  principles  is  certain  to  result  in  error 
and  often  appears  in  the  most  astonishing  distortions  of 
weight.  We  must  assume  that  they  are  eliminated  in 
the  following  experiments.* 


*The  flipping  of  the  coin  is  another  type  of  precaution.  It 
may  seem  useless,  but  it  is  indeed  very  essential  in  order  to 
forestall  any  tendency  in  the  observer  to  make  some  inference, 
whether  true  or  false,  as  to  what  the  next  order  shall  be.  Sup- 
pose that  the  experimenter  should  determine  the  order  arbitrarily, 


WEBER'S  LAW  95 

2.  The  Least  Perceptible  Difference. — With  the  dif- 
ferential weight  which  in  Exp.  1  gave  the  nearest  to 
75  per  cent  correct  judgments,  make  100  consecutive 
trials.    Record  1  for  right  or  x  for  wrong  in  each  trial. 

3.  The  Least  Perceptible  Difference  in  the  Double 
Weight. — Put  the  glass  used  into  the  other  one. 
Double  the  differential  weight.  With  this  doubled 
weight  and  doubled  increment  make  100  trials  in  the 
same  manner  as  in  Exp.  2.  Compare  the  per  cent  of 
right  cases  in  Exp.  2  and  Exp.  3.  If  Weber's  law 
applies,  the  per  cent  of  error  should  be  approximately 
equal  in  the  two  cases. 

There  are  mathematical  formulae  by  which  we  may 
calculate  from  the  above  results  what  increment  is 
needed  in  order  to  yield  any  particular  degree  of  cer- 
tainty. It  is  customary  to  use  75  per  cent  of  right 
judgments  as  a  norm  or  standard,  as  it  lies  half-way 
between  no  knowledge  and  absolute  certainty  in  this 
method.     Thus,  if  the  glass  in  Exp.  2  weighs  200  grams 

that  is,  as  he  felt  it  would  run  by  chance,  and  suppose  that  he 
had  given  the  order  "Second  heavier"  three  times  in  succession, 
would  not  the  observer  require  more  than  an  ordinary  degree 
of  assurance  before  he  would  pronounce  a  fourth  one  also  of  the 
same  order?  Yet  according  to  chance,  and  in  the  flipping  of 
the  coin,  the  number  of  times  head  has  been  up  has  not  the 
slightest  influence  on  the  next  throw.  On  account  of  our  com- 
munity of  ideas  there  is  always  a  more  or  less  subconscious  tend- 
ency present  to  anticipate  the  order  of  a  so-called  chance  series 
which  is  determined  by  one  human  will  for  another. 

Another  important  variable  is  the  bodily  attitude  taken  by 
the  observer  at  the  table.  The  attitude  of  attention  is  a  bodily 
attitude  of  muscular  tension.  If  the  observer  rests  against  the 
back  of  the  chair  he  will  make  a  much  poorer  record  than  if  he 
sits  up  with  body  erect  and  firm,  bending  his  head  gently  toward 
the  lifting  hand. 


96  WEBER'S  LAW 

and  the  differential  weight  is  12  grams,  and  this  ratio 
(6  :100)  gives  72  per  cent  of  right  judgments;  then,  by 
referring  to  a  simple  table,*  we  find  that  the  increment 
must  be  14  grams  in  order  to  yield  a  certainty  of  75 
per  cent  right  jiidginents.  This  computation  is  not 
needed  in  the  present  case  because  we  may  here  compare 
the  percentages  directly. 

Working  with  compact  hard-rubber  blocks,  which  are 
more  favorable  than  the  glasses  for  fine  discrimination, 
the  average  constant  for  a  good  observer  is  about  1 :21:. 
The  ratio  obtained  in  this  test  is  probably  considerably 
larger,  mainly  for  two  reasons — the  bulkiness  of  the 
glass,t  and  the  lack  of  practice  of  both  experimenter  and 
observer. 

Similar  ratios  may  be  worked  out  for  different  con- 
ditions in  this  sense  and  for  different  senses.  Each 
individual  has  his  own  ratio,  which  is  an  expression  of 
his  personal  equation. 

The  principle  of  its  application  is  illustrated  in  Fig. 
13,  which  is  drawn  for  the  constant  ratio  1 :24.  16,  25, 
50,  64,  etc.,  represent  selected  standards  and  .6,  1.0, 
2.0,  2.6,  etc.,  the  respective  increments  that  would  be 
just  perceptible. 

This  illustration  and  the  above  experiment  have 
reference  to  sensation-difference.     To  be  more  specific, 

*  Sanford,  "Experimental  Psychologj^"  p.  354 ;  or  Titchener, 
"Experimental  Psychology,"  Quantitative,  Instructors'  Manual,  p. 
288. 

t  The  more  compact  the  weiglit  is  the  finer  the  discrimination 
will  be.  The  discrimination  will  be  finer  if  a  thick  glass  is  used 
rather  than  a  thin  one,  because  for  the  thin  glass  the  bulk  is  pro- 
portionally greater  than  the  weight.  Both  glasses  seem  to  be 
lighter  than  they  really  are. 


WEBEK'S  LAW 


97 


the  law  stated  in  the  first  paragraphs  might  be  restated 
thus :  ^'To  increase  the  sensation-difference  in  arithmet- 
ical ratio,  it  is  necessary  to  increase  the  stimulus-dif- 
ference in  geometrical  ratio."  There  is  a  parallel  aspect 
of  Weber's  law  which  has  reference  in  a  more  direct 
way  to  sensation-magnitudes,  greater  than  the  least 
perceptible:  ''To  increase  the  sensation  in  arithmetical 
ratio,  it  is  necessary  to  increase  the  stimulus  in  geo- 
metrical ratio."  This  latter  form  of  the  law  has  great 
practical  significance  in  our  classification  of  magnitudes 
by  sense-perception. 


Fig.  13. 

Suppose  we  have  a  thousand  pebbles  which  range  in 
weight  from  1  gram  up  to  100  grams  and  we  are  re- 
quired to  sort  them  into  five  piles,  according  to  weight, 
so  divided  that  we  shall  be  equally  sure  for  each  pile 
that  the  sorting  is  right.  If  we  could  resort  to  the  use 
of  accurate  scales,  the  piles  would  range  in  arithmetical 
ratio ;  each  pile  would  cover  a  range  of  20  gTams.  But 
not  so  when  we  judge  the  weight  by  lifting.  Weber's 
law  enables  us  to  predict  what  the  grouping  should  be. 


98  WEBER'S  LAW 

An  excellent  illustration  of  this  second  aspect  of  the 
law  is  found  in  the  astronomer's  classification  of  the 
stars.  Stars  are  classified  into  a  comparatively  small 
number  of  groups,  usually  fifteen,  according  to  their 
perceived  magnitudes.  Astronomers  assume  that  this 
classification  follows  Weber's  law;  namely,  that  the 
physical  magnitudes  (the  amounts  of  light  emitted)  do 
not  stand  in  a  direct  arithmetical  ratio,  but  in  a  geomet- 
rical ratio,  in  the  grouping.  Each  group  is  supposed  to 
stand  in  a  certain  ratio  in  the  following  group,  say  1 :10. 

A  psychologist  attempted  to  verify  this  hypothesis. 
He  produced,  in  the  psychological  laboratory,  artificial 
stars  whose  physical  magnitudes  could  be  measured,  and 
then  he  grouped  these  empirically  into  '&ve  groups  on 
the  basis  of  perceived  magnitude  and  ascertained  their 
average  candle-power  by  physical  measurements.  The 
results  ran  as  follows : 

Magnitude,  or  group I        II       III      IV       V 

Average  candle-poiver  ....269     146       83       45       21 

When  one  considers  the  crudeness  of  a  measurement  of 
this  kind,  one  feels  that  these  results  show  a  fair  approx- 
imation to  the  law.^ 

Another  type  of  demonstration  of  Weber's  law  may 

*  There  is  at  least  a  very  close  analogy  to  Weber's  law  in  any 
practical  grouping  of  the  stars.  Thus  from  Kapte^Ti's  recent 
work  we  learn  that  within  a  sphere  the  radius  of  which  is  560 
light-years  there  will  be  found: 

times  the  light  of  our  sun 


1  star  giving 

from  100,000 

to  10,000 

26  stars   " 

10,000 

"  1,000 

1,300  "  .   •' 

1,000 

100 

22,000  "•   " 

100 

10 

140,000  " 

10 

1 

430,000  " 

1 

0.1 

650,000  " 

0.1 

0.01 

WEBER'S  LAW  99 

be  made  in  terms  of  discrimination-time ;  that  is,  the 
time  that  it  takes  to  perceive  a  difference.  It  rests  on 
the  postulate  that  if  differences  are  equally  difficult  to 
perceive,  the  discrimination-time  for  all  such  cases 
should  be  the  same.  Take,  for  example,  an  increment 
of  one  tenth  on  different  weights.  There  is  an  ap- 
paratus in  the  psychological  laboratory  which  consists 
of  a  system  of  weights  and  balances  which  may  be 
attached  to  an  instrument  that  measures  time  in 
hundredths  of  a  second.  To  verify  the  law,  we  might 
measure  the  discrimination-time  for  an  increment  of 
1  gram  on  10,  5  grams  on  50,  9  grams  on  90,  etc. ;  and,  if 
the  law  holds,  the  discrimination-times  should  be  equal. 
We  may  take  a  good  illustration  of  the  same  type 
from  sight — the  perception  of  the  difference  in  the 
length  of  lines.  Suppose  we  have  three  sets  of  lines, 
rig.  14,  and  we  consider  the  middle  one  in  each  group 


t-^-^ 


Fig.  14. 


the  standard  for  that  group.  We  see  in  the  figure  that 
the  longer  and  the  shorter  lines  differ  from  the  standard 
by  one  fifth  in  all  cases.  Therefore,  the  difference 
should  be  equally  clear  in  all  the  cases,  according  to 
Weber's  law.  To  measure  the  discrimination-time,  we 
arrange  the  apparatus  so  that  a  compared  line  is  ex- 
hibited immediately  after  the  standard  line,  and  then 
measure  for  each  group  the  time  it  takes  the  observer  to 
perceive  whether  the  compared  line  is  longer  or  shorter 
than  the  standard.     If  the  law  holds,  other  things  being 


100  WEBER'S  LAW 

equal,  this  discrimination-time  should  be  equal  for  all 
the  standards  within  a  normal  range  so  long  as  the 
ratio  is  constant. 

These  three  demonstrations  of  Weber's  law — the  ap- 
plication to  the  least  perceptible  difference,  the  applica- 
tion to  the  classification  of  larger  differences  in  sense- 
magnitudes,  and  the  application  to  discrimination-time 
— might  be  repeated  in  various  respects  for  other  senses. 

We  know  this  world  in  terms  of  four  aspects  of  ex- 
perience, which  are  the  four  attributes  of  sensation, 
namely,  quality,  intensity,  duration,  and  extensity. 
Weber's  law  is  primarily  a  law  of  the  intensity  of  sensa- 
tions, but  it  applies  in  some  respects  to  each  of  the  other 
attributes. 

It  is  generally  conceded  that  the  law  applies  approx- 
imately to  sensation-intensities  in  all  the  senses.  We 
have  drawn  our  experimental  illustrations  from  the 
kinsesthetic  sensations  in  the  perception  of  weight.  The 
classification  of  the  stars  is  an  illustration  from  the 
intensity  of  light.* 

A  clear  case  of  the  operation  of  Weber's  laAv  is  found 
in  the  intensity  of  sound.'  It  is  perhaps  equally  rigid 
for  the  intenstity  of  pressure  sensations.  It  has  been 
demonstrated  within  a  narrow  range  for  taste  and  smell. 
Although  it  has  not  been  worked  out  fully  for  the 
intensity  of  pain  and  temperature  sensations,  it  prob- 
ably applies,  to  some  extent,  there  also. 

*  Fechner's  cloud  experiment  is  the  classical  illustration  in 
terms  of  the  intensity  of  light,  or  brightness.  It  is  to  the  effect 
that  if  we  look  at  a  partly  clouded  sky  and  select  a  spot  where 
we  can  just  detect  a  difference  in  the  shading  of  the  two  clouds 
by  the  naked  eye  and  then  look  at  this  through  darkening  glasses 
of  different  densities,  the  difference  will  remain  equally  clear. 


WEBER'S  LAW  101 

The  operation  of  the  law  in  the  other  sense-attributes 
is  not  so  clear.  It  has  been  demonstrated  for  visual 
qualities  (color),  for  arm-si^ace,  eye-movements,  the 
duration  of  sounds,  etc.,  but  even  where  it  applies  to 
sense-attributes  other  than  intensity  it  has  reference 
•to  sense-magnitude. 

The  most  general  evidence  of  the  law  is  in  terms  of 
the  least  perceptible  difference,  as  in  the  above  experi- 
,ments  on  weight-discrimination.  Its  application  to 
larger  sense-magnitudes  is  always  more  doubtful. 

The  law  can  apply  only  within  a  middle  or  normal 
•  range  of  sensation-intensities  in  any  sense.  It  does  not 
hold  for  very  faint  sensations,  nor  for  excessively  strong 
sensations. 

Much  depends  upon  the  method  of  the  test.  Thus, 
the  application  of  the  law  to  lines.  Fig.  14,  is  much  more 
likely  to  give  a  positive  demonstration  by  the  discrimi- 
nation-time test  than  by  the  classification  test ;  indeed, 
we  should  hardly  expect  any  evidence  of  it  by  the  classi- 
fication method,  because  that  method  introduces  factors 
which  may  interfere  with  its  operation.  We  must  al- 
ways bear  in  mind  that  every  case  of  discrimination  is  a 
complex  operation  depending  upon  scores  of  variables, 
and  the  law  could  at  best  apply  absolutely  only  to  one 
set  of  conditions. 

The  greatest  gain  in  an  experiment  of  this  sort  should 
be  in  the  revelation  of  the  complexity  and  the  interrela- 
tions of  mental  laws  even  in  such  a  simple  operation  as 
the  lifting  of  a  weight.  Such  revelations  help  us  to 
analyze  and  understand  our  daily  activities  and  should 
result  in  greater  efficiency.     We  follow  Weber's  law 


102  WEBER'S  LAW 

unconsciously  in  many  of  our  well-regulated  actions  in 
which  we  are  guided  by  our  senses. 

Aside  from  the  demonstration  of  Weber's  law,  these 
experiments  illustrate  a  common  form  of  measurement 
in  all  the  senses;  namely,  the  determination  of  the  least, 
perceptible  difference   (I.  p.  d.).^     The  two  most  ele-« 
nientary  forms  of  measurement  in  all  the  senses  are  (1) 
the  threshold   of  sensitivity   and    (2)    the   /.   j).   d.   or 
threshold  of  discrimination.     In  measuring  sensitivity 
we  determine  the  smallest  quantity  of  any  stimulus — a, 
color,  a  pressure,  an  odor,  a  sound,  etc. — that  can  be 
sensed.     In  measuring  discrimination  w^e  determine  the^ 
smallest  increase   (or  decrease)   that  can  be  perceived 
on  any  given   strength  of  stimulus.       The   former   is 
chiefly  a  measure  of  the  delicacy  of  the  organism,  while 
the    latter    is    chiefly    a    measure    of   the    intellectual 
capacity  for  using  sense-differences.     Thus,  if  one  ob- 
server obtained  the  discrimination  ratio  1 :12  and  the 
other  1 :1S  in  the  above  test,  we  have  in  these  ratios 
a  measure  of  the  relative  usefulness  of  the  sense  of 
weight  for  the  two  persons. 

The  I.  p.  d.  may  be  used  as  a  sort  of  foot-rule  in  the 
quantitative  study  of  a  great  variety  of  processes.  Thus, 
with  it,  we  may  measure  features  of  fatigue,  rhythm, 
attention,  memory,  mental  development,  race  dif- 
ferences, the  effect  of  a  stimulant,  the  power  of  emu- 
lation, etc.,  provided  always  that  we  bear  in  mind  that 
in  such  cases  we  measure  only  one  feature,  the  discrimi- 

*The  term  "just  noticeable  difference"  [j.  n.  d.)  is  often  used 
in  place  of  I.  p.  d.;  so  also  is  the  term  "discrimination  limen" 
{d.  L),  many  authors  using  the  term  "limen"  for  threshold. 


WEBER'S  LAW  103 

nation,  and  that  our  conclusions  must  not  go  beyond 
this.  To  illustrate  the  reservation,  suppose  that  the 
experimenter  sets  himself  the  task  of  determining  what 
the  mental  effect  of  a  cup  of  coffee  is.  Among  other 
measurements  he  may  include  the  discrimination-tests 
in  the  various  senses  and  for  different  attributes  in 
each  sense,  and  after  a  long  series  of  measurements  he 
should  be  able  to  say:  My  discrimination  in  such  and 
such  activities  is  heightened  to  such  and  such  a  degree 
for  such  and  such  a  period  after  drinking  coffee,  and 
then  there  is  a  reaction  which  shows  at  such  and  such  a 
time  in  such  and  such  a  degree  for  such  and  such  of  the 
activities. 


CHAPTEK  IX 
MENTAL  IMAGES 

For  One. 

The  problem  is  to  determine  the  capacity  for  vivid- 
ness of  mental  images.  In  perception,  which  we  have 
studied  so  far,  the  object  is  present  to  sense.  We  see 
the  color,  hear  the  sound,  feel  the  cold  point,  etc. ;  that 
is,  we  refer  the  mental  picture  to  its  object.  In 
memory,  imagination,  and  the  various  stages  of  think- 
ing, the  object  is  not  present,  but  the  mental  picture  is 
present  as  in  percei^tion,  although  usually  less  integral, 
less  vivid,  less  enduring,  and  less  distinct.  This  mental 
picture  which  re-presents  the  object  is  the  mental 
image.* 

To  illustrate  the  fact  of  imagery,  recall  your  break- 
fast-table as  you  sat  down  to  it  this  morning.  What  is 
it  that  you  recall  ?  Is  it  merely  the  names  for  things 
and  qualities,  or  is  it  their  images  ?  The  whiteness  of 
the  china  and  the  linen,  the  brightness  of  the  silver,  the 
form  of  the  sugar-bowl,  the  taste,  the  odor,  the  temper- 
ature, and  the  hardness  or  softness  of  the  cereal, — how 

*  "Images,  along  with  sensations,  constitute  the  materials  of 
all  intellectual  operations;  memory,  reasoning,  imagination,  are 
acts  which  consist  of  grouping  and  coordinating  images,  in  ap- 
prehending the  relations  already  formed  between  them,  and  in 
reuniting  them  into  new  relations."      (Binet.) 

104 


MENTAL  IMAGES  1U5 

do  these  arise  in  your  memory  ?  Can  you  image  only 
in  certain  senses  ?  Or  are  all  these  experiences  abstrac- 
tions to  you  ?  If  they  are,  in  what  terms  do  you  re- 
member their  names  ? 

If  we  could  compare  answers  to  such  questions  as 
these,  we  should  find  the  most  astonishing  individual 
differences  in  capacity  for  types  of  imagery.  One  per- 
son is  eye-minded,  another  is  ear-minded.  One  lives  in 
a  world  of  vivid  imagery,  another  lives  in  a  dull  and 
somber  world  of  vagaie  abstractions  and  names  for 
things.  One  has  an  accurate,  serviceable  memory, 
another  has  a  '^miserable"  memory.  One  has  an  apti- 
tude for  geometry,  another  for  music.  One  has  a 
fertile,  constructive  imagination,  another  is  as  devoid 
of  imagination  as  a  desert  is  devoid  of  vegetation.  One 
is  sensitive  and  responsive,  another  is  deliberate  and 
unmoved. 

If  we  were  blind,  or  should  walk  about  with  our  eyes 
closed,  the  world  would  be  different  to  us  from  what  it 
is  now.  The  congenitally  blind  person  is  not  only  de- 
prived of  the  ability  to  see  color,  form,  and  motion,  but 
he  is  also  deprived  of  the  power  to  remember,  imagine, 
and  think  of  colors  and  visual  forms  and  movements. 
His  world  is  not  a  visible  world.  Similarly,  the  world 
to  the  deaf  person  is  a  world  without  sound.  Helen 
Keller  lives  in  a  world  in  which  there  is  neither  light, 
nor  color,  nor  sound.*  Her  world  is  a  world  of  touch, 
muscle  sensations,  smell,  taste,  temperature,  and  pain. 

*  Helen  Keller  retained  normal  sensibility  until  she  was  nine- 
teen months  old,  and  she  says:  "A  person  who  has  ever  seen  will 
retain  images  of  light  throughout  life;  sight  and  sound  are,  how- 
ever, of  little  if  any  use  to  me." 


106  MENTAL  IMAGES 

Yet  she  lives  a  more  intelligent  and  cultured  life  than 
the  average  college  graduate. 

This  shows  what  great  and  varied  resources  the  mind 
has.  Our  worlds  of  memory  and  imagination  may  be 
built  of  vastly  varied  materials,  although  to  serve  the 
same  purpose.  Miss  Keller  judges  character  by  the 
touch  of  the  hand ;  so  also  do  many  seeing  persons. 
Many  persons  have  normal  ears  for  hearing,  but  can 
recall  things  heard  only  in  terms  of  the  other  senses.  A 
comparatively  small  number  of  persons  can  remember 
coffee  in  terms  of  taste  and  smell. 

The  differences  we  notice  in  the  traits  of  individuals 
are  not  due  so  much  to  differences  in  sensory  endow- 
ment as  to  differences  in  the  endowment  of  capacity  for 
representing  sensory  experiences  in  realistic,  efficient, 
and  economic  imagery.  Although  Aristotle  said  that 
one  cannot  think  without  a  sensible  image,  it  is  only  a 
generation  ago  that  the  fact  of  mental  imagery  attracted 
much  attention.  Taine,  Sir  Francis  Galton,  Fechner, 
Charcot,  and  others  found  that  they  had  vivid  visual 
imagery,  and  made  investigations  which  revealed  the 
fact  that  such  imagery  is  almost  universal.  These  in- 
vestigations led  also  to  the  discovery  that  some  persons 
have  auditory  imagery.  Later,  more  general  inquiry 
revealed  the  fact  that  it  is  even  possible  to  have  images 
in  terms  of  each  and  all  the  senses. 

The  main  body  of  this  exercise  is  devoted  to  a  test  of 
the  capacity  for  vividness  of  imagery. 

This  is  a  distinct  exercise  in  introspection.  It  is  best 
to  keep  the  eyes  closed  as  you  introspect.  If  the  ob- 
ser\^er  does  not  have  strong  imagery  he  may  be  lost  in 


MENTAL  IMAGES  107 

the  effort  to  create  an  image  out  of  the  retinal  light. 
To  avoid  this,  it  is  best  to  think  of  the  object  as  in  a 
distant  place ;  for  example,  the  rose  on  the  bush. 

Sometimes  the  image  comes  in  the  most  realistic 
way  when  it  comes  without  effort  as  a  sort  of  a  reverie 
image  which  ]3asses  the  mental  horizon.  As  a  rule,  it  is 
best  not  to  direct  the  attention  primarily  to  the  detail 
of  the  image,  but  rather  to  the  effort  to  recall  the  fact ; 
when  the  fact  comes  into  consciousness  the  character 
of  the  image  may  be  observed. 

Fix  clearly  in  mind  and  use  as  consistently  as  pos- 
sible the  following  scale  of  degrees  of  vividness : 

0.  'No  image  at  all. 

1.  Very  faint. 

2.  Faint. 

3.  Fairly  vivid. 

4.  Vivid. 

5.  Very  vivid. 

6.  As  vivid  as  in  perception. 

Answer  the  following  questions  by  writing  after  the 
number  of  the  question  the  number  which  denotes  the 
degree  of  vividness  characteristic  of  your  image.*     In- 

*  To  some  students  this  exercise  will  be  entirely  too  easy ;  to 
others,  equally  bright,  it  will  seem  like  an  impossible  task.  The 
reason  for  this  difference  lies  in  the  fact  that  one  person  may 
have  such  vivid  imagery  that  it  is  as  easy  for  him  to  answer 
the  first  question  as  to  say  whether  or  not  he  sees  a  rose  which 
is  held  before  his  open  eyes,  while  to  another  person  the  task 
seems  unreasonable,  for  with  the  best  effort,  he  cannot  see  the 
slightest  evidence  of  any  concrete  image,  nor  does  he  know  what 
it  is  to  have  such  an  image.  These  are  extreme  types,  between 
which  normal  types  range.  The  student  who  finds  difficulty 
should  not  be  discouraged.  The  aim  of  this  exercise  is  not  to 
develop  imagery,  but  to  test  the  actual  normal  capacity. 


108  MENTAL  IMAGES 

stead  of  taking  the  questions  in  the  order  given, 
follow  the  order:  I  1,  II  1,  III  1,  IV  1,  V  1,  VI  1, 
VII  1,  VIII  1,  I  2,  II  2,  III  2,  IV  2,  etc.,  I  3,  II  3, 
III  3,  IV  3,  etc.  Introspective  notes  to  supplement 
the  numerical  answers  are  very  desirable. 

1.  Visual. — 1.  Can   you   image   the   color   of — (a) 

A  red  rose?  (h)  A  green  leaf?  (c)  A  yellow 
ribbon?      (d)  A  blue  sky? 

2.  Can  you  image  the  brightness  of — (a)   A  white 

teacup?  (h)  A  black  crow?  (c)  A  gray 
stone  ?      (d)  The  blade  of  a  knife  ? 

3.  Can  you  image  the  form  of — (a)  The  rose?      (h) 

The  leaf?      (c)  The  teacup?      (d)  The  knife? 

4.  Can  you  form  a  visual  image  of — (a)  A  moving 

express  train  ?  (h)  Your  sharpening  of  a  pencil  ? 
(c)  An  up-and-down  movement  of  your  tongue  ? 

5.  Can  you  image  simultaneously — (a)   A  group  of 

colors  in  a  bunch  of  sweet  peas?  (h)  Colors, 
forms,  brightnesses,  and  movements  in  a  land- 
scape view  ? 

6.  Can  you  compare  in  a  visual   image — (a)    The 

color  of  cream  and  the  color  of  milk?  (h)  The 
tint  of  one  of  your  finger-nails  with  that  of  the 
palm  of  your  hand  ? 

7.  Can  you  hold  fairly  constant  for  ten  seconds — 

(a)  The  color  of  the  rose  ?  (h)  The  form  of  the 
rose  ? 
II.  Auditory. — 1.  Can  you  image  the  sound  of — 
(a)  The  report  of  a  gun?  (h)  The  clinking  of 
glasses?  (c)  The  ringing  of  church-bells?  (d) 
The  hum  of  bees  ? 


MENTAL  IMAGES  109 

2.  Can  YOU  image  the  characteristic  tone-quality  of — 

(a)  A  violin  ?  (h)  A  cello  ?  (c)  A  flute  ?  (d) 
A  cornet? 

3.  Can  you  repeat  in  auditory  imagery  the  air  of — 

(a)  Yankee  Doodle?      (h)  America? 

4.  Can  you  form  auditory  images  of  the  intensity  of 

a  violin- tone — (a)  very  strong;  (h)  strong; 
(c)  weak;  (d)  very  weak? 

5.  Can  you  form  auditory  imagery  of  the  rhythm 

of — (a)  The  snare-drum  ?      (h)  The  bass-drum  ? 

(c)  ''Dixie/'  or  other  air  heard  played?  (d) 
"Tell  me  not  in  mournful  numbers"  spoken  by 
yourself  ? 

III.  Motor. — 1.  Can  you  image,  in  motor  terms, 
yourself — (a)  Rocking  in  a  chair?  (b)  Walk- 
ing down  a  stairway?  (c)  Biting  a  lump  of 
sugar?      (d)   Clenching  your  fist? 

2.  Does  motor  imagery  arise  in  your  mind  when  you 

recall — (a)  A  waterfall?  (h)  A  facial  ex- 
pression of  fear  ?      (c)   The  bleating  of  sheep  ? 

(d)  Two  boys  on  a  teeter-board  ? 

3.  Aside  from  the  actual  inceptive  movements,   do 

you  get  motor  imagery  when  recalling — (a)  A 
very  high  tone?  (b)  A  very  low  tone?  (c) 
Words  like  'Taderewski/'  ''bubble,"  "tete-a- 
tete,"  "Hurrah !"  ? 

4.  Can  you  form  motor  images  of — (a)   An  inch? 

(&)  A  yard?      (c)  A  mile  ? 

5.  Can  you  form  a  motor  image  of — (a)  The  weight 

of  a  pound  of  butter?  (b)  Your  speed  in  run- 
ning a  race  ?     (c)  The  speed  of  an  arrow  ? 


no  MENTAL  IMAGES 

IV.  Tactual. — 1.  Can  you  form  a  tactual  image 
of  the  pressure  of — (a)  Velvet?  (h)  Smooth 
glass?      (c)  Sandpaper?      (<i)  Mud? 

2.  Can  you  form  tactual  imagery  of  the  following 
impressions  made  in  the  palm  of  your  hand — 
(a)  The  size  of  a  certain  coin?  (6)  The  form 
of  the  same  coin?  (c)  The  direction  of  a 
line  traced  by  a  pencil-point  ?  (d)  The  inter- 
mittent touch  of  a  vibrating  body  ? 

8.  Can  you  form  tactual  imagery  of — (a)  The  flow 
of  water  against  the  finger?  (h)  The  sensation 
from  a  pressure  spot  ?  (c)  The  weight  of  a 
particular  coin  in  the  hand  ? 

V.  Olfactory. — 1.   Can  you  image  the  odor  of — • 

(a)    Coffee?      (&)    Camphor?      (c)   An  onion? 
(d)  Apple-blossoms  ? 
2.  Can  you  image  odors  from — (a)  A  meadow?     (h) 
A  confectioner's  shop  ? 

VI.  GusTATOEY. — 1.  Can  you  image  the  taste  of — 
(a)  Sugar?  (h)  Salt?  (c)  Vinegar?  (d) 
Quinine  ? 

2.  Can  you  image  the  taste  of — (a)  An  apple? 
(h)  A  chocolate  cake  ?     ( c)  Beefsteak  ? 

VII.  Thermal. — 1.  Can  you  image  the  coldness 
of — (a)  Ice  cream?  {h)  A  draught  of  cold 
air?  (c)  The  sensation  from  the  stimulation  of 
a  cold  spot  ? 

2.  Can  you  image  the  warmth  of — (a)  Hot  tea  ?  (h) 
A  warm  poker?  (c)  A  warm  bath  ?  (d)  The 
sensation  from  the  stimulation  of  a  warmth 
spot? 


MENTAL  IMAGES 


111 


VIII.  Pain. — 1.  Can  you  secure   a  sensory  image 

of  the  pain  of — (a)  The  prick  of  a  pin?      (6) 

Running  your  finger  along  the  edge  of  a  sharp 

knife?      (c)    A   toothache    or    headache?      (d) 

The  stimulation  of  a  pain  spot  ? 

Compute  the  averages  for  all  the  answers  in  each 

of  the  experiments  I  to  VIII.     Lay  off  a  plot  in  pencil 

as  in  Fig.  15,  eight  blocks  long  and  six  high,  and  number. 


5 
4 
3 
2 

1 


II         HI         1/  V 

Fig.  15. 


VI         VII      VIII 


as  in  this  figure,  where  the  vertical  series  represents  the 
scale  of  vividness  from  0  to  6,  and  the  horizontal  series 
represents  the  senses  I  to  VIII.  Plot  the  averages  with 
ink  in  a  curve  as  in  Fig.  15.^ 

Thus,  we  have  arrived  at  a  very  simple  and  telling 
graphic  representation  of  the  observer's  capacity  for 
vividness  of  imagery.     It  is,  of  course,  relative  to  this 


*This  model  curve  is  purely  arbitrary,  and  does  not  purport  to 
represent  any  particular  type  of  observer.  It  is  inserted  merely  to 
show  how  to  make  the  graphic  representation  of  the  results.  It 
shows  an  average  of  4.4  for  I,  1.8  for  II,  3.8  for  III,  .8  for  IV,  etc. 


112  MENTAL  IMAGES 

particular  set  of  questions ;  a  different  set  of  questions 
covering  the  same  ground  might  change  the  curve.  A 
set  of  questions  is  legitimate  only  in  so  far  as  it  covers 
the  principal  types  of  imageable  facts  in  a  fair  distribu- 
tion of  tests. 

You  are  fully  aware  of  the  unreliability  of  the  results. 
They  are  unreliable  for  at  least  two  reasons.  First, 
the  power  of  imagery  varies  with  numerous  conditions 
and  attitudes.  The  method  of  measuring,  crude  as  it  is, 
is  fully  fine  enough  to  be  commensurate  with  the  con- 
stancy of  the  fact  tested.  Second,  the  results  are  un- 
reliable because  you  were  untrained.  This  sort  of 
introspection  is  a  severe  test  upon  the  power  of  dis- 
criminative attention  and  is  made  particularly  difficult 
and  uncertain  for  the  beginner  on  account  of  the  novelty 
and  complexity  of  the  undertaking.  Faithful  practice 
in  the  training  of  any  particular  type  of  imagery  is 
usually  rewarded  with  rapid  improvement  and  in- 
creased confidence  in  judgments.  The  difficulties  and 
uncertainties  are  greatest  where  there  is  poverty  of 
imagery. 

(  Such  factors  as  vividness,  stability,  and  integrity  of 
Jthe  image  do  not  necessarily  vary  together.  An  image 
may  be  very  vivid  but  flitting ;  it  may  be  complete  but 
faint.  For  a  full  study  of  the  capacity  the  above  ques- 
tions miglit  be  repeated  and  answered  in  turn  with 
reference  to  each  of  the  variables  in  the  image.  This 
same  exercise  might  be  used  for  the  determination  of 
such  factors  as  the  stability  of  the  image,  completeness 
of  the  image,  effort  in  producing  it,  etc.  In  such  cases, 
words  representing  stability,  completeness,  effort,  etc., 


MENTAL  IMAGES  113 

would  be  substituted  for  the  word  vivid  in  the  scale: 


thus:  'No  image,  very  fluctuating,  fluctuating,  fairly 
stable,  stable,  very  stable,  as  stable  as  in  perception. 

It  is  customary  to  speak  of  organic  sensations  and 
organic  images,  but  that  is  rather  misleading;  for  we 
then  refer  to  sensation-complexes  or  perceptions.  Thus, 
the  organic  feeling  of  movement  in  pointing  a  finger 
may  be  reduced  to  sensations  of  pressure  and  strain  in 
the  joints,  muscles,  and  tendons.  Hunger  may  ordi- 
narily be  reduced  to  a  complex  of  pressure,  pain,  strain, 
and  temperature.  It  is  of  course  as  much  easier,  as  it 
is  more  superficial,  to  say  that  one  has  an  image  of 
hunger  than  to  trace  the  pressure-pain-strain-temper- 
ature elements  in  the  composite  image. 

The  sense  of  equilibrium  is  not  included  in  the  above 
list,  for  the  reason  that  it,  more  than  any  other  sense, 
acts  automatically  and  therefore  plays  a  very  small  role 
in  consciousness. 

I^ormally  the  image  is  in  the  same  sense  as  the 
original  experience ;  for  instance,  the  memory  of  a  color 
comes  as  a  color  image,  the  memory  of  pressure  comes 
as  a  pressure  image,  the  memory  or  imagination  of  taste 
comes  as  a  taste  image,  and  even  when  present,  it  is 
often  overshadowed  by  the  image  in  another  sense.  But 
this  is  not  always  so.  One's  memory  of  running  blind- 
folded may  be  recalled  entirely  in  visual  terms;  one's 
memory  of  the  taste  of  coffee  may  come  in  no  more 
significant  imagery  than  sight. 

Dream-life  is  almost  purely  a  life  of  imagery;  and 
dream  images  are  for  many  persons  as  vivid  as  the  per- 
ceptions of  waking  life.     They  even  transcend  them, 


114  MENTAL  IMAGES 

for  we  often  dream  of  more  brilliant  colors,  more  beauti- 
ful harmonies,  more  graceful  movements,  than  we  ever 
perceive  in  waking  life. 

Hallucinations  are  common  occurrences,  although  but 
few  persons  observe  or  report  them.  Who  has  not 
heard  a  sound  where  there  was  no  sound,  smelled  some- 
thing where  there  was  nothing  to  smell,  seen  something 
where  there  was  nothing  visible  ?  These  hallucination 
images  are  often  vivid ;  their  very  vividness  makes  them 
deceptive. 

This  test  pertains  merely  to  the  capacity  for  imaging 
in  terms  of  the  respective  senses  and  does  not  necessarily 
reveal  the  dominant  type.  Indeed,  should  the  capacity 
be  limited  to  but  one  or  two  senses,  or  should  there 
be  no  capacity  at  all,  the  type  would  be  determined, 
but  such  a  condition  is  not  a  common  occurrence.  We 
not  infrequently  find  a  record  for  pain  images  as 
high  as  that  for  color  images,  but  this  does  not  signify 
that  the  w^orld  is  equally  one  of  pain  and  of  color 
to  the  possessor  of  that  curve ;  for  pains  do  not  occur 
so  frequently  as  colors,  and  it  is  customary  to  trans- 
late all  imagery  into  the  terms  of  one  sense  wdien- 
ever  possible. 

There  are  numerous  methods  in  vogue  for  determin- 
ing the  type  of  imagery.  One  of  these  is  to  proceed  as 
follows : 

Write,  in  a  column,  a  list  of  thirty  words  that  give  scope^  for 
imagery  in  the  different  senses  about  as  in  ordinary  conversation; 
for  example,  dog,  field,  waves,  beefsteak,  sunset,  war,  springtime, 
accident,  apple-blossoms,  desert.  Cover  the  list  with  a  card  and 
expose  one  word  at  a  time.  As  soon  as  the  word  has  been  seen, 
look  away  and  note  the  imagery  which  comes  to  represent  the 
word  and  the   object   it  denotes.     Thus,   the   word  dog  may  be 


MENTAL  IMAGES  115 

grasped  in  terms  of  visual,  auditory,  and  motor  images,  and  the 
dog  may  be  imaged  as  a  baying  hound  close  on  the  scent  of  a 
fox,  these  aspects  being  experienced  in  terms  of  visual,  audi- 
tory, motor,  tactual,  and  pain  images  respectively.  The  record 
would  then  read: 

Word.  Word  Image.  Object  Image. 

Dog     Visual-auditory-motor      Visual-auditory-motor-tactual-pain. 

If  a  list  of  siTch  words  is  made  fairly  representative, 
tlie  records  will  furnish  a  basis  for  an  estimate  of  the 
relative  frequency  of  the  images  of  each  sense,  both  in 
word  memory  and  object  memory.  These  records  may 
be  reduced  to  percentages. 

To  show  the  significance  of  the  sense  through  which 
the  word  is  first  received,  the  series  should  be  repeated, 
by  having  the  words  read  aloud  to  the  observer.  For 
most  persons  this  will  cause  a  radical  change  in  the 
imagery. 

The  type  of  imagery  may  also  be  determined 
roughly  from  answers  to  questions  like  these : 


Into  what  sense  do  you  normally  translate  your  sensory  expe- 
riences? In  terms  of  what  imagery  do  you  normally  remember  a 
person?  A  place?  A  date?  An  abstract  quality?  Can  you  se- 
cure images  in  any  other  sense  than  sight  without  also  having  a 
visual  image?  (This  question  may  be  adapted  to  the  other 
senses.)  Do  you  visualize  the  situations  as  you  read  a  story? 
Do  you  find  geometry  difficult?  Do  you  recall  music  readily? 
Have  you  a  good  sense  of  rhythm?  Are  you  moved  by  realistic 
descriptions?  Do  you  dream  much  and  vividly?  Is  there  any 
sense  in  which  you  cannot  recall  having  had  a  dream  image? 
Is  your  word  imagery  conspicuous  and  helpful? 


Among  the  curious  idiosyncrasies  which  come  out  in 
a  test  like  this  is  that  of  s^Tisesthesia.  Some  persons 
invariably   project    numbers    upon    forms    or    skeletal 


116  MENTAL  IMAGES 

shapes  which  may  be  maintained  constant  thronghont 
life.  Others  have  colored  hearing;  when  they  hear 
or  remember  a  tone,  it  seems  to  have  color.  There 
are  numerous  other  forms  of  synsesthesia,  and  these 
differ  very  much  in  force  and  complexity.  Some 
fairly  well-marked  form  of  it  may  be  found  in  from 
5  to  10  per  cent  of  the  peoj^le  in  a  community. 
The  explanation  is  to  be  found  in  the  fact  that  we 
have  a  tendency  to  give  fulness  to  perceptions  and 
images.  Synsesthesia  is  simply  a  specialized  form  of 
this  tendency  and  should  be  regarded  merely  as  a 
habit.* 

Reverie  also  gives  opportunity  for  the  flow  of  realistic 
imagery.  The  procession  of  images  moves  on  without 
effort  as  though  it  were  controlled  by  some  external 
machinery.  Reverie  and  concentrated  attention  are 
the  antipodal  types  of  normal  experience.  Our  or- 
dinary life  is  a  blending  of  the  two,  and  even  the 
most  reflective  student  will  find  upon  introspection 
that  reverie  plays  by  far  the  larger  part.  The  read- 
ing of  a  passage,  the  solving  of  a  problem,  the  ex- 
amination of  a  situation,  or  any  other  such  activity 
as  requires  concentration  of  attention  is  accompanied 


*  Answers  to  questions  like  the  following  reveal  the  presence  or 
absence  of  the  principal  forms  of  syn?esthesia :  "Do  you  think 
of  particular  colors  in  connection  with  letters  of  the  alphabet, 
or  numerals,  or  proper  names,  or  musical  sounds,  or  any  other 
unusual  connection?  Do  you  think  of  numerals  or  names  of 
months,  days,  or  years,  or  of  any  series  of  words  as  arranged  in 
any  particular  shapes,  like  circles,  squares,  zigzags,  or  very  long 
lines?  Do  single  numerals,  letters,  musical  notes,  etc.,  make  you 
think  of  different  shapes?  Do  you  especially  like  or  dislike  any 
numerals,  letters,  etc.  ?  Do  numerals,  letters,  etc.,  seem  to  you  to 
be  like  people  ?"     ( Calkins,  American  Journal  of  Psychology,  VII. ) 


MENTAL  IMAGES  117 

by  broad  streams  of  reverie  images.  These  irrele- 
vant images  constitute  what  we  call  distraction  or 
mind-wandering;  they  are  often  more  vivid  and 
coercive  than  the  images  obtained  from  the  object  of 
attention. 


Califop,^\^---^' 


CHAPTEE  X 

ASSOCIATION 

For  Two* 
The  problem  is  to  determine  certain  characteristics 
of  association;  namely,  rapidity,  kind,  reinforcement, 
error,  and  persistence. 

1.  Rapidity. — Call  out  a  key-word,  for  example 
"star",  and  give  O  exactly  8  seconds,  counting  from 
the  moment  of  the  giving  of  the  key-word,  in  which  to 
speak  as  many  disconnected  words  as  he  possibly  can. 
Let  O  write  them  down  in  a  vertical  column,  beginning 
with  the  key-word,  while  they  are  fresh  in  his  memory. 
Secure  five  records,  using  as  many  key-words,  t  Find 
the  total  number  of  words  in  each  column  excluding  the 
key-word,  and  divide  8  by  that  number  to  get  the  aver- 
age duration  of  each  association. 

This  experiment  might  be  called  chain  reaction  in 
free  association.     It  has  three  objects:  first,  to  secure 

*  Provide  coins  or  disks  for  Exp.  4,  and  a  paper  bag  and 
weights  for  Exp.  5. 

f  Speed  is  the  aim.  O  must  not  stop  to  consider  the  fitness, 
significance,  kind  of  association,  or  anything  else  which  may  im- 
pede the  rapidity  of  speaking.  There  is  a  great  temptation  to 
hesitate.  No  series  should  be  considered  successful  imless  0  has 
spoken  at  least  six  words  in  the  allotted  time.  The  only  limita- 
tion on  words  is  that  they  shall  be  disconnected;  that  is,  they 
cannot  be  a  sentence,  a  familiar  list  of  words,  a  prepared  list,  or 
any  series  of  words  which  have  a  fixed  connection  or  sequence. 

118 


ASSOCIATION  119 

lists  of  words  under  definite  conditions  for  use  in 
the  following  experiments;  second,  to  measure  the 
rapidity  of  association ;  and  third,  to  give  a  glimpse  of 
the  existence  and  natural  flow  of  associations. 

The  observer  is  convinced  that  the  associations  came 
much  faster  than  he  could  express  them.  It  is  equally 
clear  to  him  that  he  did  not  speak  as  fast  as  mere  words 
could  be  uttered;  there  was  a  continual  groping  to  ex- 
tract one  out  of  the  many  more  or  less  remotely  avail- 
able words. 

An  average  observer  should  secure  a  list  of  about  ten 
words  in  8  seconds ;  the  average  time  for  each  word 
would  then  be  .8  of  a  second. 

Each  word  represents  a  complex  process  or  act.  The 
average  time  of  such  acts  varies  very  much  with  dif- 
ferent conditions  and  individuals.  We  speak  of  one  as 
having  a  quick  reaction-time,  and  another  as  having  a 
slow  reaction-time.  One  is  mentally  alert,  another 
mentally  sluggish,  and  still  another  is  erratic.  Such 
individual  differences  can  be  measured  in  great  detail 
by  reaction  experiments  in  association.* 

The  more  completely  the  observer  followed  the  in- 
structions and  abandoned  himself  in  the  battle  of 
imagery,  the  more  surprising  some  of  the  words  were  to 
him.  At  first  thought  there  may  be  neither  sense  nor 
order  in  them.  Yet  every  word  came  according  to  law. 
These  laws  we  shall  now  proceed  to  trace. 

Associations  are  modes  of  connection  between  per- 

*  In  the  laboratory,  chronoscopes  are  used  which  record  the 
time  in  hundredths  or  thousandths  of  a  second.  One  single  act 
at  a  time  is  studied,  and  the  conditions  are  so  varied  that  thii 
act  may  be  separated  into  its  component  elements. 


120  ASSOCIATION 

cepts,  images,  and  ideas.  There  is  difference  of  opinion 
in  regard  to  the  number  and  kinds  of  association,  but 
this  is  largely  a  matter  of  how  fine  distinctions  we  wish 
to  make.  For  the  present  purpose  it  is  convenient  to 
posit  three  kinds  of  association,  namely,  contiguity, 
similarity,  and  contrast,  which  include  all  possible 
kinds.'^'  These  three  kinds  of  association  are  spoken  of 
as  laws.  The  law  of  contiguity  asserts  that  things 
wdiich  have  occurred  together  in  time  or  space  tend  to 
recur  together.  The  law  of  similarity  asserts  that 
things  which  are  alike  tend  to  recall  one  another.  The 
similarity  may  be  of  any  kind, — color,  form,  sound, 
odor,  motion,  use,  etc.  The  law  of  contrast  asserts  that 
opposites  tend  to  recall  one  another.  There  may  be  as 
many  modes  of  contrast  as  there  are  of  similarity.  The 
use  of  this  classification  may  be  illustrated  best  by  an 
actual  case.  The  following  record  was  made  by  the 
author  when  writing  this  section.     The  key-word  was 

"fig." 

Fig  "Fig  suggested  apple    (simil.).     Tree  struggled  to 

appear  as  a  separate  word  (eontig«),  but  finally 
fused  with  apple  and  formed  a  compound  word  de- 
Apple-tree  noting  three  distinct  images, — apple,  tree,  blossoms 
(contig. ).  The  incongruity  of  apples  and  blossoms 
on  the  same  tree  was  not  noted.  The  images  of 
flowers  were  soon  accompanied  by  images  of  bees 
(contig.),  but  as  the  images  came  much  faster  than 
Honey  I  could  speak  the  words,  the  image  of  honey   (con- 

tig.) was  uppermost  in  consciousness  before  I 
could  begin  to  speak  the  next  word.  The  image 
of    honey    made    me    irresistibly    conscious    of    the 

*  This  view  is  most  serviceable  for  the  elementary  analysis 
of  a  concrete  experience,  regardless  of  what  ultimate  theory  of 
association  one  may  have.  Thorndike's  discussion  of  association 
in  his  "Elements  of  Psychology"  would  supplement  this  exercise 
very  well. 


ASSOCIATION 


121 


question  why  honey  should  have  followed  flower 
(contig. ),  and  there  came  to  me,  as  a  reply,  eon- 
Juice  sciousness  of  the  fact  that  honey  is  the  juice  of 
a  flower  (contig.  and  simil.).  This  bit  of  forbidden 
reasoning,  very  complex,  reminded  me  that  the 
Sweetness  characteristic  quality  of  flower-juice  is  sweetness 
(simil.).  (Our  imagery  is  much  richer  than  our 
vocabulary,  and  our  associations  are  often  couched 
in  words  coined  at  the  moment  to  serve  their  pur- 
pose, for  instance  'flower-juice'  ,  although  they 
may  be  of  doubtful  value  for  currency  in  speech.) 
There  followed  a  bombardment  by  a  mob  of  images 
which  struggled  for  recognition  as  representatives 
of  sweet  juices  or  extracts  (simil.).  The  image  of 
sugar  was  distinctly  in  the  foreground  (simil.), 
Malt  but  before  I  could  speak,  I  thought  of  malt  as  an 
extract  which  contains  sugar  (simil.).  Then  a 
whole  flock  of  extract-bottles  in  varied  colors  and 
forms  flew  before  my  mental  eye  (simil.).  They 
had  so  equal  recognition  of  attention  that,  for  the 
moment,  I  could  not  decide  to  discriminate  in  favor 
of  one  or  another  in  the  group  by  mentioning  it, 
so  I  compromised  by  including  them  all  and  said 
extract  ( simil.  by  whole  and  part ) .  But  when  I 
heard  the  w^ord  extract  I  thought  T'll  take 
vanilla'  (simil.),  and  saw  myself  seated  on  a  high 
chair  consuming  a  soda  in  the  front  of  a  drug- 
store with  a  fountain  to  the  left,  fruit-dishes  to  the 
right,  and  in  front  of  me  a  white-jacketed  waiter 
Clerk  (clerk),  with  a  supercilious  air  and  limited  brain 
capacity.  (This  scene  was  all  one  composite  image 
w^hich  was  suggested  by  soda-water  ( contig. ) . 
The  last-mentioned  feature  in  this  impression 
brought  a  feeling  of  compunction  which  took  the 
Phrenologist  form  of  the  question,  Mm  I  a  phrenologist  (simil. 
and  contr. ),  that  I  profess  to  judge  a  man's 
brain?'  There  followed  a  jumble  of  more  or  less 
fragmentary  images  of  long  hair,  a  phrenological 
chart,  the  word  'fake' ,  etc.,  but  these  overran  the 
time  limit." 


Extract 


Vanilla 


There  are  two  particularly  conspicuous  tendencies  in 
this  introspection.  The  first  is  that,  although  the  ob- 
server was  free  to  use  any  part  of  speech,  nouns  were 
used  exclusively.  The  reason  for  this  lies  in  the  fact 
that  economy  of  speech  has  made  the  object-image  the 


122  ASSOCIATION 

most  available  antecedent  to  a  speech-word.  The  ob- 
jects, i.e.,  images  of  objects,  seem  to  be  the  things  in 
consciousness.  The  other  peculiarity  is  that  there  was 
only  one  clear  case  of  association  by  contrast.  Contrast 
is  a  principle  which  should  be  used  only  for  effect,  and 
in  the  ordinary  flow  of  images  it  is  not  frequent. 

If  one  has  a  good  grasp  of  images,  they  may  be  traced 
in  much  greater  detail. 

2.  Kinds  of  Association:  Primary  Laws. — Let  O 
trace  the  chain  of  associations  in  one  of  the  lists  he  has 
and  write  out,  on  the  plan  of  the  above  specimen,  an 
introspection  showing  which  of  the  three  kinds  of  as- 
sociation operated  in  the  transition  from  image  to 
image.*  Make  the  report  even  more  detailed  than  the 
model,  and  point  out  as  many  links  of  association  as 
possible  among  the  images  of  which  the  words  represent 
only  a  few. 

An  introspection  of  this  kind  reveals  to  the  observer 
something  of  the  richness  and  connectedness  of  such  a 
simple  and  apparently  incoherent  mental  act.  There 
was  no  trouble  in  seeing  why  each  word  came ;  there 
was  a  reason  for  every  word.  The  words  do  not  express 
the  full  chain  of  the  processes,  not  even  all  the  clearly 
conspicuous  images,  but  simply  one  here  and  there,  for 
the  flow  of  images  is  more  rapid  than  thought  and  in- 
comparably more  rapid  than  speech.  There  were  rea- 
sons for  every  image,  though  few  can  be  tracd.  And, 
furthermore,  the  images  did  not  stand  out  isolated  and 

*  Some  observers  may  prefer  to  make  a  new  list  in  order  to 
have  the  chain  of  associations  fresh  in  the  mind. 


ASSOCIATION  123 

stripped,  but  were  supported  by  a  background  and 
bridging  material  of  more  or  less  undifferentiated 
imagery  and  non-integrated  mental  activity.  There 
was  a  reason  for  each  element  in  this. 

Two  facts  of  most  profound  significance  are  there- 
fore impressed  upon  the  observer  in  this  experiment: 
all  images  flow  according  to  law ;  the  number  of  primary 
laws  is  surprisingly  small.  Similarity  and  contrast  are 
usually  considered  inseparable.  Each  of  these  also  in- 
volves an  element  of  contiguity.  This  has  led  some  to 
say  that  there  is  only  one  law  of  association.  But  these 
three  phases  vary  so  much  in  relative  prominence  that  it 
is  helpful  to  trace  the  dominating  aspect,  as  in  this 
experiment. 

But  the  question  arises,  what  determined  which 
particular  image  should  come  forth  by  the  law  of  con- 
tiguity when  there  was  a  vast  number  of  possibilities  of 
the  same  kind  ?  Why  does  apple  and  not  a  score  of 
equally  similar  things  follow  fig?  Or,  in  similarity, 
why  does  sweetness  suggest  sugar  and  not  one  of  the 
many  other  sweet  things  ?  Why  does  darkness  suggest 
black  horse  and  not  some  of  the  many  other  dark  things  ? 
The  ansAvers  to  these  questions  are  to  be  found  in  the 
secondary  laws  which  are  laws  of  neural  action  or  habit. 
Four  of  these  are:  primacy,  frequency,  intensity,  and 
recency."^  Other  things  being  equal,  the  first  or 
primary  association  will  dominate ;  other  things  being 
equal,  the  most  frequently  repeated  association  will 
dominate ;  other  things  being  equal,  the  most  impressive 

*  Calkins,  "Association",  Monograph  Supplement  to  the  Psy 
chological  Review,  No.  2,  1896. 


124  ASSOCIATION 

or  intense  association  will  dominate ;  other  things  being 
equal,  the  most  recent  association  will  dominate. 

These  four  secondary  laws  may  operate  within  any  of 
the  three  primary;  that  is,  contiguity,  similarity,  and 
contrast.  There  is  thus  established  a  complex  mecha- 
nism of  forces  Avhich  cooperate  or  counteract  in  various 
ways  and  to  various  degrees. 

We  may  think  of  the  primary  law^s  as  kinds  of  ties  or 
bonds  for  the  image,  and  the  secondary  laws  as  power 
applied  to  each  tie.  Each  image,  ordinarily  has  a  large 
number  of  ties.  Usually  all  three  kinds  are  repre- 
sented, and  each  is  supplied  with  more  or  less  power. 
The  image  brought  up  by  the  key-word  above  had  a  rich 
supply  of  these  ties.  The  next  image  which  came  to  the 
front  came  because  it  was,  as  it  were,  most  effectively 
tied  up  with  the  other.  This  is  illustrated  in  the  fol- 
lowing introspection  which  is  supplementary  to  the  one 
quoted  above : 

"Fig  suggested  apple  because  apple  is  the  most  common  (freq.) 
specimen  of  the  kind  of  thing  a  fig  is,  a  fruit.  Apple  suggested 
tree  because  they  have  been  experienced  together  frequently 
(freq.).  Tree  suggested  blossoms  because  I  had  been  looking  for 
blossoms  on  the  cherry  trees  this  morning  (rec. ).  Blossoms  sug- 
gested bee  because  bees  are  frequently  seen  with  blossoms  and 
their  presence  has  an  exciting  interest  (freq.  and  int.).  Bee 
suggested  honey  because  bee  and  honey  are  thought  of  as  cause 
and  effect  (freq.).  Honey  suggested  juice  of  a  flower  because 
the  image  of  honey  had  followed  the  image  of  flowers  (rec). 
Flower- juice  suggested  sweetness  because  sweetness  is  the  prin- 
cipal characteristic  of  flower-juice  or  honey  (in ten.  and  freq.). 
Sweetness  suggested  the  mass  of  images  of  sweet  things  because 
there  is  a  tendency  for  the  mind  to  think  the  abstract  in  terms 
of  the  concrete  (freq.).  Sugar  came  to  the  front  from  these 
because  it  is  the  commonest  of  sweet  things  ( freq. ) ,  Sugar  sug- 
gested malt  because  sugar  was  thought  of  as  an  extract  and  malt 
is  a  common  form  of  extract  which  contains  sugar  (freq.).  Ex- 
tract was  present  in  the  image  of  malt  ( rec.  and  freq. ) .  Vanilla 
came  to  the  front  because  it  is  one  of  the  most  familiar  extracts 


ASSOCIATION  12.5 

(freq. ).  Vanilla  suggested  ice-cream  soda  on  account  of  my 
frequent  choice  of  that  flavor  in  soda  ( freq. ) .  Soda-water  sug- 
gested myself  and  the  whole  setting  in  the  drugstore  (prim,  ami 
freq.).  Clerk  was  named  from  the  many  objects  in  the  setting 
because  the  image  represented  something  living  and  active  in 
relation  to  m3^self  ( inten.  and  freq. ) .  Phrenologist  was  drawn 
out  from  the  situation  of  my  judging  brain  capacity  on  account 
of  the  strangeness  and  incongruity  of  the  idea  ( inten. ) .  The 
images  came  very  much  faster  than  words  could  be  spoken,  and 
there  was  a  distinct  tendency  to  fit  the  word  to  the  image  which 
was  just  coming  into  consciousness  at  the  moment  that  I 
could  begin  to  articulate  the  next  word.  For  this  reason  many 
very  strongly  associated  images  were  deprived  of  opportunity  for 
expression." 

3.  Reinforcement ;  Secondary  Laws. — Let  O  retrace 
the  chain  of  associations  in  the  same  list  as  in  Exp.  2, 
and  write  out  an  introspection  showing,  as  in  the  above 
specimen,  where  and  how  the  four  secondary  laws, 
primacy,  frequency,  intensity,  and  recency,  operated, — 
not  only  for  these  words,  but  for  all  the  recognized 
images  which  the  words  represent  only  in  part. 

The  primary  laws  are  qualitative ;  they  denote  kinds 
of  association.  The  secondary  laws  are  quantitative; 
they  denote  force  or  magnitude  of  a  quality.  The  two 
invariably  operate  together.  Had  it  not  been  for  the 
sake  of  clearness,  the  introspections  of  Exps.  2  and  3 
should  have  been  A\T:^itten  out  together,  stating,  for  ex- 
ample, that  in  a  given  instance  the  law  of  contiguity 
operated  in  several  directions,  but  a  certain  one  of  these 
became  dominant  by  the  law  of  frequency. 

The  associations  in  the  list  quoted  above  were  in  a 
light,  agreeable  vein.  The  observer  accounts  for  this 
on  the  ground  of  '^emotional  congruity."  Emotional 
congruity  is  one  of  a  number  of  so-called  laws  of  as- 
sociation which  are  neither  primary  nor  secondary. 
They  might  properly  be  described  as  unanalyzed  com- 


126  ASSOCIATION 

plexes  of  association.  Thus,  according  to  this  law,  one 
thinks  of  good  and  pleasant  things  when  one  is  well  and 
happy,  and  this  in  turn  makes  one  better  and  happier; 
when  one  is  blue,  the  disagreeable  things  come  to  mind. 
!N^ow,  a  state  of  happiness  or  a  state  of  misery,  if  re- 
duced to  the  constituent  elements  in  so  far  as  they  are 
cognitive,  would  probably  resolve  itself  into  a  very 
intricate  complex  of  the  above  primary  and  secondary 
laws,  or  laws  of  a  similarly  elementary  order. 

One  of  the  easiest  ways  of  getting  material  for  the 
study  of  images  and  their  modes  of  connection  is  simply 
to  sit  down  and  relax  one's  self  and  allow  a  passive  flow 
of  imagery,  as  in  reverie,  for  a  few  seconds,  and  then  go 
over  it  and  retrace  the  connections.  Another  good  way 
is  to  analyze  a  specific  act  of  remembering  or  thinking ; 
for  instance,  let  the  observer  recall  his  last  boat-ride,  or 
answer  the  question  ''What  is  courage  ?"  Each  of  these 
instances  can  be  reduced  to  a  definite  network  of  the 
operations  of  these  primary  and  secondary  laws  of 
association."^ 

4.  Errors  of  Association — Take  a  dollar,  two  half- 
dollars,  two  quarter-dollars,  two  nickels,  and  two 
dimes  f  and  arrange  them  edge  to  edge  in  a  row,  with 
the  dollar  in  the  middle  and  the  other  coins  ranging  in 
opposite  directions  away  from  the  dollar  in  the  order  of 
diminishing  size.  Let  O  take  such  a  position  that  his 
eyes  are  directly  over  the  dollar,  the  row  pointing  toward 


*  Work  out  these  two  examples  if  time  permits, 
f  Circles  cut  any  size  but  varying  in  about  the  same  proportion 
as  the  coins  may  be  used  in  place  of  the  coins. 


ASSOCIATION  127 

him,  and,  without  sighting  or  measuring,  straighten  the 
row  of  coins  so  that  one  side  tangent  to  all  the  coins  will 
seem  to  be  a  straight  line.  When  he  is  satisfied  that 
the  line  is  as  straight  as  he  can  make  it,  without  sight- 
ing or  measuring,  lay  a  straight-edge  alongside  and 
measure  in  millimeters  the  amount  of  misplacement 
of  each  coin. 

The  normal  observer  will  arrange  the  coins  so  that 
what  seems  to  be  a  straight  line  is  really  a  gracefully 
curved  line.  The  straight-edge  touches  only  the  dollar, 
and  the  other  coins  retreat  from  it  by  distances  inversely 
proportional  to  their  size.  This  is  true  only  for  the 
normal  and  careful  observer;  an  unfaithful  observer 
may  read  this  paragraph  before  he  performs  the  ex- 
periment and  try  to  correct  for  the  error. 

The  explanation  for  this  normal  error  lies  in  the  fact 
that  when  we  make  one  judgment  we  are  invariably 
beset  by  a  number  of  other,  often  irrelevant,  judgments. 
In  this  case  the  observer  was  asked  to  make  one  side 
straight ;  but  he  could  not  do  that  without  having  more 
or  less  dimly  in  the  background  of  consciousness  a  line 
through  the  center  of  the  coins  and  a  line  on  the  other 
side  of  the  coins.  The  presence  of  these  associations 
influenced  his  judgment  on  the  straightness  of  the  one 
line  in  question. 

Fig.  16  illustrates  the  same  principle.  The  middle 
sections  of  the  five  bars  are  parallel;  they  do  not  look 
parallel  because  we  cannot  entirely  dissociate  direction 
of  the  end  lines  from  the  direction  of  the  middle 
sections. 

Normal  life,  in  all  its  phases  and  all  the  degrees  of  its 


128 


ASSOCIATION 


complexity,  is  full  of  errors;  the  greatest  number  of 
these  are  errors  of  association.  The  association  need 
not  be  a  conscious  one ;  it  may  have  been  reduced  to  the 
simplest  law  of  neural  habit. 

Popularly  we  say  ''I  had  something  else  on  my  mind." 
Thus,  in  reading  we  read  largely  by  the  context;  and 
for  this  reason  there  are  very  few  good  proof-readers. 
A  good  author  may  read  a  proof-sheet  a  half-dozen  times 
without  noticing  that  a  senseless  word,  not  to  speak  of 
an  error  in  spelling,  is  flagTantly  evident.     The  good 


Fig.  16. 

proof-reader  has  mastered,  to  a  considerable  extent,  the 
power  of  suppressing  meaning-associations."^ 

5.  Irrepressibility  of  Association. — Inflate  a  large 
paper  bag  and  tie  it  up.  Place  this  bag  on  one  hand 
of  the  observer  and  put  coins,  nails,  or  any  other  heavy 
material  into  the  other  hand  until  O  judges  that  the 
weights  in  the  two  hands  are  equal.  Let  him  change 
hands  and  verify  his  judgments  until  he  is  satisfied. 
Then  weigh  the  bag  and  the  coins  separately  and  record 
the  results. 

There   is    a   general   tendency    toward    harmony   of 


7 


*  In   reading  this   last   word   in   the   copy,   the  author   read   it 
'meaningless  associations." 


ASSOCIATION  129 

properties  in  nature.  In  the  long  run,  large  objects  are 
heavier  than  small  objects.  This  observed  fact  has 
crystallized  under  the  principle  of  frequency  into  a 
neural  habit  which  acts  without  our  attending  to  it. 
This  association  is  a  very  economic  principle,  for  it 
helps  us  to  adjust  our  efforts  to  our  tasks.  Without 
thinking  of  it,  we  make  the  proper  differences  in  ad- 
justment of  muscles  for  the  lifting  of  a  peck  of  apples 
and  a  bushel  of  apples.  Now,  when  a  large  object  like 
the  bag  is  extraordinarily  light,  the  association  causes 
us  to  put  forth  too  great  effort  in  lifting  it  and  this 
maladjustment  leads  to  underestimation  of  the  weight 
of  the  bag.  Similarly,  coins  are  small  for  their  weight, 
and  the  same  association  probably  leads  us  to  make  too 
delicate  an  adjustment  for  the  lifting  of  these;  this 
maladjustment  leads  to  an  overestimation  of  the  weight 
of  small  objects.  If  we  now  compare  the  actual  w^eight 
of  the  bag  with  that  of  the  coins,  w^e  find  that  the  normal 
observer  has  selected  coins  which  weigh  only  from  a  half 
to  a  tenth  as  much  as  the  bag.  Here  is  the  real  answer 
to  the  old  quibble :  which  is  heavier,  a  pound  of  lead  or  a 
pound  of  feathers  ?  That  this  illusion  persists  after 
training  and  accurate  knowledge  of  the  actual  weights 
is  an  illustration  of  the  fact  that  habits  of  association 
continue  irrepressibly  in  the  face  of  sense  and  reason. 

We  have,  in  this  and  foregoing  chapters,  marshalled 
before  our  mind's  eyes  the  material  in  the  structure  of 
our  knowing  processes.  The  materials  are  the  percep- 
tions, images,  and  ideas  ;*   the  structure  is  their  modes 

*  All  mental  life  is  activity ;  perceptions,  images,  and  ideas  are 
always  processes. 


130  ASSOCIATION 

of  connection — the  associations.  But  just  as  in  a  build- 
ing the  material  is  all  there  is,  so  here  the  perceptions, 
images,  and  ideas  constitute  the  mental  states,  the 
cognitive  life.  Association  merely  denotes  the  ways  in 
which  the  materials  are  joined  together  in  the  mental 
framework. 

Education  consists  in  the  development  of  associations. 
To  the  uneducated,  the  grain  of  sand  does  not  suggest 
the  great  number  of  geological  forces  that  brought  it 
together ;  it  may  not  even  suggest  the  economical  uses  to 
which  it  might  be  put. 


CHAPTER   XI 

MEMOKY 

For  Two. 

The  problem  is  to  determine  certain  factors  in  the 
capacity   for   memorizing   geometrical    figures.       Two 


P  K- 


-T 


T 


d  "V  d  T 


Fig.  17. 


r 


styles  of  figures  will  be  used.  One  the  style  shown  in 
Fig.  17,  and  the  other  the  style  shown  in  Fig.  18.     Let 

131 


132  MEMOEY 

the  first  experimenter  use  the  former  style,  and  the 
second  the  latter.  As  the  illustrations  in  the  book  con- 
tain the  material  which  is  to  be  memorized,  each  person 
must    refrain    rigorously    from    examination    of    the 


V 


^^y- 


\ 


V7         ^^^       X 


^^-.      :s-.        _A 


\ 


x 


^     ^v  \ 

Fig.  18. 

material  assigned  to  the  other.  This  is  imperative. 
Both  may  proceed  independently  to  prepare  materials 
for  the  experiment,  as  follows : 

Set  A :  Select  nine  of  the  figures  of  your  style  and 
draw  them  neatly  by  freehand  in  a  single  vertical  col- 
umn in  your  note-book. 

Set  B :  Arrange  the  same  nine  figures,  on  another 
page,  into  a  regular  parallelogram  with  three  figures  in 
each  row  horizontally  and  vertically. 


MEMOKY  133 

Set  C :  Eearrange  the  same  nine  figures,  on  another 
page,  into  the  same  kind  of  a  parallelogram  but  in  a 
'radically  different  order;  leave  no  figures  in  the  same 
position  as  in  B. 

All  the  figures  have  certain  features  in  common :  * 
each  figure  is  composed  of  three  lines ;  the  lines  are  all 
straight;  two  lines  are  equally  long,  and  the  third  is 
half  as  long  as  these;  the  two  long  lines  always  adjoin 
each  other;  the  lines  join  either  at  the  end  or  in  the 
middle;  no  line  is  crossed;  no  two  figures  are  alike. 
The  angles  in  one  style  are  right  angles,  and  in  the  other 
angles  of  45°  or  the  supplement  of  45.° 

1.  Memorizing  the  Form  of  Figures. — Allow  O  to 
see  the  figures  in  Set  A  exactly  ten  seconds,  in  a  uni- 
form and  favorable  position,  and  then  let  him  reproduce 
as  many  of  these  as  he  can,  regardless  of  the  order  in 
the  column.  Examine  the  reproduction  to  see  if  there 
is  any  error  or  omission  f  and  then  cover  it  with  some 
opaque  object.  Show  him  the  set  again  for  ten  seconds 
and  let  him  reproduce  as  before.  Repeat  this  pro- 
cedure until  O  has  reproduced  the  form  of  all  the 
figures  correctly,  regardless  of  the  order  or  position  in 
the  column. 

Check  those  that  are  right  in  each  reproduction,  and 


*  In  verifying  this  refer  only  to  the  sets  of  figures  you  have 
selected  and  constructed. 

f  After  examining  a  reproduction,  E  can  say  only  "Right"  or 
"Wrong".  If  any  figures  are  wrong  in  form,  0  must  discover  it 
for  himself. 

X  In  case  of  excessive  difficulty  the  experiment  may  be  left  iDCom« 
plete,  say  at  twelve  trials. 


134 


MEMOKY 


write  in  tabular  form  the  number  of  correct  figures 
for  each  trial.  Plot  a  curve  of  the  results,  as  in 
Fig.  19,  where  the  numbers  at  the  bottom  denote  the 
successive  trials,  and  the  numbers  at  the  side  denote  the 
number  of  figures  that  remain  unlearned. 

Let  O  record  observations  as  to  method  of  learning 
the  figures,  groupings,  disturbing  factors,  peculiar  aids 


9 
8 

\ 

\ 

7 
6 
5 
4 

3 
o 

\ 

\ 

\ 

\ 

\ 

\ 

7 
0 

\ 

1 

\ 

12          3         4         5         6          7         8 

Fig. 

19. 

such  as  the  use  of  imagery  schemes,  etc. — in  short, 
anything  which  may  aid  in  the  interpretation  of  the 
curve. 

One  of  the  fundamental  requirements  for  an  experi- 
ment, as  we  have  seen,  is  that  the  problem  shall  be  re- 
duced to  its  elements ;  only  one  element  at  a  time  may 
be  varied,  and  all  other  elements  and  conditions  must 


MEMOEY  135 

be  kept  constant.  This  is  an  ideal  which  is  never  fully 
attained,  yet  the  value  of  an  experiment  may  often  be 
measured  or  tested  by  this  criterion. 

This  experiment  is  an  illustration  of  a  fair  control  of 
conditions  in  a  memory  test.  The  observer  started  with 
a  full  and  adequate  knowledge  of  certain  specifications 
as  to  the  number,  the  length,  the  straightness,  and  non- 
crossing  of  the  lines,  the  adjacency  of  the  lines,  the 
place  of  joining,  the  magnitude  of  the  angle,  the  number 
of  figures,  and  the  absence  of  repetition.  These  are  all 
features  in  the  memorizing  of  the  form  of  the  figures. 
They  could  be  learned  by  accurate  discrimination  in 
repeated  observation,  but  to  have  left  them  unmentioned 
in  the  present  experiment  would  have  complicated  it 
and  made  it  practically  worthless.  The  experiment 
begins  with  the  supposition  that  these  are  known ;  hence 
they  are  eliminated  from  the  memory  task  which  is 
before  the  observer.* 

With  all  these  factors  under  control,  the  problem  was 
reduced  to  the  specific  task  of  learning  the  forin  of  the 
figures.  Other  desirable  features,  such  as  the  order  of 
the  figures,  were  excluded. 

Then  followed  the  control  of  conditions  for  learning 
and  recording.  The  exposure  of  the  figures  was  made 
definite, — ten  seconds  at  a  time.  The  time  of  retention 
was  made  definite ;  the  observer  reproduced  immedi- 
ately.    The  means  of  verifying  were  limited;  the  ob- 

*  Suppose  the  observer  had  been  required  to  learn  by  observa- 
tion that  every  figure  has  three  lines,  and  that  no  two  figures 
are  alike,  and  to  learn  by  very  close  discrimination  that  the  lines 
do  not  vary  in  length  by  small  steps,  that  the  angles  are  uniform, 
that  the  place  of  the  joint  is  limited,  etc.  He  would  then  have 
faced  a  very  different  problem  from  the  present  one. 


136  MEMORY 

server  had  no  access  to  the  records  of  his  foregoing 
trials.  The  experimenter's  approval  or  disapproval  was 
uniform ;  the  experimenter  gave  no  clue  as  to  which  or 
how  many  were  wrong.  The  records  were  all  preserved, 
making  it  possible  to  trace  certain  peculiarities  in  the 
learning  process  objectively. 

Yet  the  introspective  notes  show  that  several  con- 
ditions which  might  have  been  controlled  were  not  con- 
trolled. For  example,  the  observer  might  have  been 
instructed  as  to  how  to  proceed  most  effectively  in  mode 
of  impression,  grouping,  classification,  associating,  using 
concrete  imagery,  etc.  He  might  have  been  warned  of 
certain  avoidable  difiiculties.  In  technical  experiments 
such  factors  must  also  be  isolated  and  controlled. 
There  are  two  reasons  for  not  attempting  it  here:  in 
the  natural  development  of  a  problem  these  factors 
come  out  in  introspection  first  and  are  then  taken  into 
consideration,  one  after  another,  as  they  are  revealed ; 
they  are  too  intricate  to  control  in  the  time  allotted  for 
an  elementary  experiment.  The  careful  observer  has 
seen  the  force  of  many  of  them  and  has  mentioned  them 
in  his  introspections. 

Closely  related  to  these  are  many  individual  and 
temporary  conditions  which  never  can  be  controlled  en- 
tirely. Among  such  are  the  fluctuations  of  attention, 
peculiar  associations,  temperamental  disqualification  for 
the  task,  imagery  types,  habits  of  memorizing,  etc. 

Thus  we  see  in  a  general  way  how  far  we  have  suc- 
ceeded in  complying  with  the  requirements  for  analysis 
of  the  problem  and  control  of  its  elements.  The  recog- 
nition of  difiiculties  is  the  first  step  toward  progress. 


MEMOEY  137 

This  experiment  should  serve  two  purposes:  it  should 
give  a  glimpse  of  the  complexity  of  the  conditions  that 
enter  into  a  memory  test,  and  it  should  leave  the  im- 
pression that  with  patience  and  skill  the  complex  situa- 
tion may  be  reduced  to  more  elementary  ones  which  can 
be  isolated  and  controlled. 

2.  Memorizing  the  Position  of  the  Figures. — Allow 
O  to  see  the  figures  in  Set  B  in  ten-second  exposures  and 
proceed  as  in  Exp.  1,  except  that  the  task  here  is  to 
memorize  the  positions,  the  forms  being  known  from 
Exp.  1. 

Check,  tabulate,  plot  curve,  and  write  introspections 
as  in  Exp.  1. 

This  experiment  builds  upon  the  foregoing.  The  ob- 
server acquired  a  definite  degree  of  certainty  in  the 
memory  of  the  form  of  the  figures  in  Exp.  1 ;  he  was 
just  barely  able  to  reproduce  all  the  forms  from  memory. 
These  figures,  whose  form  was  known,  were  redis- 
tributed and  the  task  was  to  memorize  their  present 
positions. 

This  task  was  made  difficult  by  the  similarity  of  the 
figures  and  their  relative  lack  of  immediate  associations 
or  names.  The  figures  were  '^stripped"  in  this 
way  to  secure  relatively  simple  and  homogeneous 
material  which  should  enable  the  observer  to  follow 
the  development  of  his  method  and  to  record  his  intro- 
spections. 

Probably  the  most  striking  fact  the  observer  learned 
was  that  he  could  not  ^'handle"  the  figures  without  en- 
riching  them   with    associations   in   concrete    imageryc 


138  MEMOKY 

lie  faced  the  same  kind  of  difficulty  as  he  would  face  in 
trying  to  remember  individually  a  dozen  hailstones,  all 
j^erceptibly  different  in  shape. 

The  observers  may  be  divided,  on  the  basis  of  these 
two  experiments,  into  two  types:  those  who  go  about  it 
by  some  sort  of  rote  method,  and  those  who  develop 
imagery  which  gives  them  something  tangible.  Both 
of  these  types  have  various  subtypes,  as  may  be  seen  in 
the  introspections.  In  general  we  may  say  that  those  of 
the  first  type  found  the  first  experiment  very  difficult 
and  the  second  even  worse ;  while  those  of  the  second 
type  soon  mastered  the  first  experiment  and  profited 
very  much  by  it  in  the  second.  An  important  exception 
may  be  noted  later. 

It  is  a  well-known  fact  that  memorizing  is  facilitated 
by  giving  meaning  to  the  new  material.  This  is  illus- 
trated in  the  remembering  of  poetry,  a  landscape,  a  face, 
an  invention,  a  work  of  art,  etc.  Such  objects  are  ex- 
ceedingly rich  in  meaning;  we  cannot  think  of  them  at 
all  except  in  terms  of  certain  meanings.  Such  material 
is  not  suitable  for  experimental  study  because  it  is  too 
complex;  there  are  too  many  possibilities  and  uncer- 
tainties. 

Nonsense  syllables,  as  buk,  miv,  pok,  dal,  etc.,  have 
been  used  extensively  on  account  of  their  supposed  lack 
of  meaning.  But  work  with  such  syllables  soon  reveals 
the  fact  that  one  cannot  memorize  ten  of  them  without 
reading  into  them  curious,  varied,  and  efficient  associa- 
tions or  meanings.  The  present  figures  are  undoubtedly 
much  freer  from  natural  associations,  yet  one  cannot 
regard   them  without   ^'feeling  into   them"    (German, 


MEMORY  139 

limeinf illilen)  motor,  visual,  tactual,  or  other  forms  of 
imagery  and  perceiving  analogies  of  various  sorts. 

Let  us  notice  some  of  the  means  at  the  command  of 
the  observer  of  the  second,  the  ingenious,  type.  He 
may  prepare  for  the  test  by  fixating  clearly  an  image 
of  the  plot  of  positions  and  then  number  these  mentally. 
He  may  make  one  of  the  specifications  the  basis  for  a 
starting-point  in  the  grasping  of  a  figure.  Thus^  knoiK=^ — 
ing  that  there  is  only  one  short  line  in  each  figure,  he 
may  classify  the  figures  with  reference  to  the  position 
of  the  short  line,  or  with  reference  to  the  type  of  figure 
formed  by  the  other  two  lines.  He  may  fix  in  each  trial 
a  group  of  similar  figures,  the  easiest  figures,  the  most 
difiicult  figures,  the  figures  in  one  line,  etc.,  and  then 
proceed  systematically  by  concentrating  on  as  many  as 
he  can  master  in  one  exposure.  He  may,  if  he  has  a 
fertile  imagination,  give  fantastic  descriptive  names  to 
the  figures,  or  make  the  situation  dramatic*  He  may 
classify  the  figures  into  the  T  and  F  types  and  then 
remember  them  as  the  one  or  the  other  upturned, 
leaning  to  the  right,  leaning  forward,  top  and  middle 
lines  interchanged,  etc.  He  will  fix  the  gToup  grasped 
deliberately  in  the  reproduction  so  that  there  shall  be 
no  danger  of  losing  any  part  of  it  when  he  gets  other 
groups  in  mind.  He  will  adhere  vigorously  to  the 
principle  adopted,  and  not  mix  methods. 

The  curve  of  learning  is  probably  of  the  same  general 
shape  here  as  in  Exp.  1. 

*Thus,  in  the  first  line  of  forms  in  Fig.  18  he  may  see  this 
episode :  The  folding  chair  gives  away  ( 1 ) ,  the  man  makes  a  dive 
(2),  he  puts  the  chair  into  a  position  for  comfort  (3),  but  soon 
finds  it  on  the  floor   (4). 


140  MEMOKY 

3.  Memorizing  the  Position  of  the  Figures  after 
Redistribution. — Allow  O  to  see  the  figures  in  Set  C  in 
ten-second  exposures  and  proceed  as  in  Exp.  2. 

Check,  tabulate,  plot  curve,  and  Avrite  introspections 
as  in  Exp.  2. 

The  object  of  this  experiment  is  to  determine  to  what 
extent  and  in  what  respect  the  observer  has  profited  bj 
the  foregoing  training.  The  extent  of  improvement  is 
shown  by  a  comparison  of  the  curves.  The  character 
of  the  cause  of  improvement  is  shown  in  the  intro- 
spections. 

Observers  of  the  first  type  find  this  experiment,  like 
the  two  foregoing  ones,  difficult,  and  show  but  little  if 
any  progress ;  wdiile  observers  of  the  second  type  make 
improvement  and  feel  the  task  growing  easier. 

Those  who  made  improvement  have  probably  re- 
corded that  they  acquired  some  power  or  insight  as  to 
means  of  grasping  the  figures  in  the  first  two  experi- 
ments. They  also  probably  acknowledge  having  ben- 
efited by  one  or  more  of  the  suggestions  in  the  dis- 
cussion of  Exp.  2.  But  the  greatest  gain  undoubtedly 
depends  upon  the  fact  that  the  observer  could  here 
place  the  figures  in  terms  of  their  position  in  Set  B, 
which  he  remembers.  Thus,  he  may  have  observed  at 
once  that  the  first  is  now  the  seventh,  the  seventh  is 
now  the  fourth,  the  second  is  now  the  fifth,  etc. 

In  any  or  all  of  the  experiments  a  person  with  natural 
ability  may  fail  to  make  good  progress  for  several  rea- 
sons. He  may  have  imdertaken  to  use  some  means 
which  are  not  suited  to  him.  He  may  change  methods 
and  thus  lose  both  by  the  discarding  and  by  the  resulting 


MEMOKY  141 

confusion.  These  and  many  like  causes  may  account 
for  the  levels  and  even  rises  in  the  curve  at  any  stage. 
They  are,  of  course,  stated  in  the  introspections,  and 
the  idiosyncrasies  of  the  curve  are  to  be  explained 
principally  by  them. 

In  foregoing  chapters  we  have  learned  something 
about  the  significance  of  individual  differences  in  sensi- 
bility, discrimination,  imagery,  and  association.  There 
are  even  greater  differences  in  memory  types.  One 
person  has  good  memory  for  names,  another  for  faces, 
another  for  poetry,  another  for  geometrical  figures,  etc. 
Here  we  have  tested  one  narrow  type  of  memory.  The 
observer's  other  memories  may  or  may  not  be  like  it. 

This  experiment  suggests  that  improvement  in  mem- 
ory consists  largely  in  learning  how  to  observe.  This 
fact  has  great  pedagogical  and  psychological  signif- 
icance. It  makes  psychological  analysis  relatively  sim- 
ple, and  gives  promise  that  a  pedagogy  of  memory 
may  be  based  upon  a  psychology  of  improvement  in 
memory. 

There  are  three  general  types  of  methods  employed 
in  experiments  on  memory :  the  method  of  reproduction, 
the  method  of  identification,  and  the  method  of  intro- 
spection of  the  memory  image.  The  above  experiments 
have  illustrated  the  first.  The  second  might  be  illus- 
trated by  experiments  on  the  memory  for  the  size  of 
circles.  A  standard  circle  is  shown ;  after  a  given  time- 
interval  a  compared  circle  which  is  either  equal  to  the 
standard  or  slightly  different  in  diameter  is  presented, 
and  the  observer  is  required  to  say  whether  it  is  equal, 
larger,  or  smaller.    By  varying  the  diameter  of  the  com- 


142  MEMORY 

pared  circles  in  small  steps  and  making  a  large  number 
of  trials  it  is  possible  to  get  a  measure  of  the  observer's 
space-memory  in  terms  of  the  error  made.  The  third 
method  is  really  not  a  method  of  measurement,  but  a 
method  of  controlling  introspection.  The  observer  sets 
himself  constant  conditions  for  observation  and  then  ob- 
serves in  repeated  trials  the  character  of  the  imagery 
and  other  factors,  much  in  the  same  way  as  in  the  above 
introspections.^ 

Memory  is  not  a  suitable  title  for  an  experimental 
problem  because  the  term  is  too  comprehensive.  It 
is  customary  to  speak  of  four  elements  in  memory: 
impression,  retention,  recollection,  and  recognition. 
These  are  in  turn  very  broad  terms.  Thus,  we  may 
have  impressions  through  the  different  senses,  imagina- 
tion, reasoning,  and  feeling,  and  all  sorts  of  combina- 
tions of  these.  AVithin  one  sense,  the  impression  may 
have  reference  to  different  attributes ;  namely,  quality, 
intensity,  duration,  and  extensity  or  space. 

The  experiment  must  be  limited  to  one  factor  at  a 
time,  as  we  have  seen.     It  may  be  a  study,  e.g.,  of  the 

*  Kuhlmann,  American  Journal  of  Psychology,  October,  1907, 
suggests  problems  from  this  third  point  of  view,  as  follows: 
"This  general  aim  is  threefold.  First,  the  analysis  of  the  mem- 
ory consciousness  into  its  elements.  What  different  kinds  of 
mental  imagery,  what  organic  sensations  and  affective  states 
occur  in  the  mind  from  the  beginning  to  the  end  of  the  process 
of  the  recall  of  a  given  thing?  Secondly,  the  determination  of 
the  function  in  the  memory  consciousness  of  each  of  these  ele- 
ments. What  is  the  order  in  which  they  appear,  of  what  use  is 
each  in  attaining  the  end  that  is  desired,  to  wit,  the  reinstate- 
ment of  the  imagery  that  is  wanted  and  the  recognition  of  this 
imagery  as  correct  or  not?  Thirdly,  since  the  end  product  of  a 
recall  process  is  often  a  memory  illusion,  a  prominent  question 
in  memory  analysis  is  that  of  the  nature  and  causes  of  these 
memory  illusions." 


MEMOEY  143 

materials  of  impression  such  as  tones,  spoken  numbers, 
noises,  colors,  distances,  etc. ;  it  may  be  a  study  of  the 
modes  of  impression,  such  as  rote,  logical  analysis, 
forced  association,  etc. ;  or  it  may  be  a  study  of  the  effect 
of  repetition,  length  of  retention,  mental  occupation, 
etc.  The  pursuit  of  any  of  these  problems  will  do  much 
to  enrich  one's  conception  of  the  orderliness,  the  beauty, 
and  the  worth  of  the  life  of  re-presentation. 


chapter  xii 
appekceptio:n^ 

For  Two. 
Apperception  is  the  meaning-aspect  of  experience. 
It  is  the  grasping  of  a  new  experience  in  terms  of  previ- 
ous experience  in  such  a  way  as  to  give  it  meaning  and 
clearness  and  to  make  it  serviceable.  Some  authors 
reduce  it  to  ''clearest  perception/'  others  identify  it 
with  '^attention  activity/'  and  still  others  look  upon  it 
as  a  classifying  or  ''pigeonholing"  process.  It  is  well  to 
keep  these  theories  in  mind.  But  apperception  is  not  a 
process  in  itself,  such  as  perception,  memory,  or  feel- 
ing; it  rather  designates  the  fusion  of  the  presentative 
with  the  representative  and  the  relating  processes  and 
all  their  affective  and  conative  tendencies,  in  the 
moment  of  a  new  experience."^ 

1.  The  Meaning-tendency. — Place  a  drop  of  ink  on 
a  clean  sheet  in  the  note-book,  place  a  sheet  of  paper  over 
it  and  press  gently  so  that  the  ink  forms  an  irregular 
blot.     Make  three  such  blots  in  each  note-book.     Let 


*  Presentation  includes  sensation  and  perception ;  representa- 
tion includes  memory  and  imagination;  and  elaboration  or  the 
relating  processes  include  conception,  judgment,  and  reasoning. 
Affection  has  reference  to  feeling,  and  conation  to  will  and  action. 

144 


APPERCEPTION  145 

each  student  write  for  each  of  these  six  *  "gobolinks" 
a  secret  list  (not  in  the  note-book)  of  three  different 
things  it  might  represent,  giving  them  in  the  order  in 
which  they  are  thought  of,  but  counting  only  such  as 
are  apt.f 

When  these  lists  have  been  completed,  without  co- 
operation or  consultation,  write  the  two  sets  of  answers 
from  the  lists  under  the  respective  dots  and  observe  (1) 
that  the  objects  suggested  may  be  very  radically  dif- 
ferent, (2)  that  the  meaning  given  is  related  to  the  ob- 
server's interests,  recent  experience,  habits,  etc.,  and 
(3)  that  the  actual  physical  blot  seems  to  change  with 
the  change  in  meaning. 

The  objects  suggested  may  be  widely  different ;  but 
when  one  observer  sees  the  other's  list  he  is  ordinarily 
able  to  see  the  same  interpretations  although  he  had  not 
seen  the  slightest  hint  of  them  before. 

If  we  had  hundreds  of  records  of  this  kind,  it  would 
be  interesting  to  compare  them  and  observe  how  they 
reflect  the  observer's  interests,  recent  experiences, 
habits,  temperament,  mental  capacity,  knowledge,  etc. 

It  is  most  significant  that  the  actual  physical  blot 
seems  to  change  radically  as  we  pass  from  one  interpre- 
tation to  another. 

The  object  in  using  the  ink-blots  is,  of  course,  clear ; 
there  is  no  intentional  design  in  them  and  they  are  free 
from  fixed  associations.  They  should  not  represent 
anything,  yet  they  do  suggest  things  in  terms  of  past 
experience  to  every  alert  mind.     The  person  who  ap- 

*  Three  in  each  note-book, 

f  Do  not  stare  at  the  figures  or  search  for  details. 


146  APPEKCEPTION 

plies  himself  to  the  study  of  these  supposedly  meaning- 
less objects  in  a  free  and  artistic  mood  gets  a  glimpse  of 
that  tendency  in  human  nature  which  justifies  the  poet 
in  saying 

".  .  .  not  the  slightest  leaf  but  trembling  teems 
With  golden  visions  and  romantic  dreams." 

The  analogy  between  the  human  eye  and  the  photo- 
graphic camera  is  instructive.  There  is  the  dark 
chamber,  the  sensitive  film,  the  lens  with  mechanism 
which  adjusts  for  clearness,  distance,  and  size,  the  iris 
diaphragm,  and  the  cap.  The  camera-maker  simply 
imitates  nature.  But  if  this  analogy  suggests  to  us  that 
the  human  eye  is  nothing  but  a  living  camera,  it  is  very 
misleading.  The  camera  copies  the  object ;  the  human 
eye,  ^^the  mind's  eye,"  interprets  the  object. 

All  perception  is  inceptive  interpretation.  Among 
different  persons  viewing  the  same  point  in  a  landscape 
under  exactly  similar  outward  conditions,  the  botanist 
sees  the  cause  for  the  shape  of  the  overhanging  tree,  the 
artist  sees  effective  shadows  for  the  setting  of  a  sketch, 
the  carpenter  sees  a  good  location  for  a  cottage,  the 
farmer  sees  the  rich  clover  going  to  waste,  and  the 
summer  girl  sees  the  location  for  a  romance.* 

"We  see  things  not  as  they  are  but  as  we  are."     (Patrick.) 

And  let  a  man  recall  what  he  has  seen  in  a  familiar 
landscape  as  a  child,  as  a  ball-player,  as  a  lover,  as  a 

*  Speaking  of  a  certain  ink-blot,  one  writer  says :  "To  the 
hunter  it  is  a  beaver  or  a  woodchuck;  to  the  naturalist,  a  hedge- 
hog or  a  flounder,  according  as  his  mind  has  been  most  directed 
to  land  animals  or  fish;  to  the  mason,  a  trowel;  to  the  keeper 
of  pets,  an  Angora  cat."     (Colgrove.) 


APPERCEPTION  147 

real-estate  investor,  as  a  naturalist — in  happy  moods  or 
in  gray  moods,  in  company  or  alone.  Xo  matter  how 
constant  the  outward  features,  he  has  always  seen  in  the 
landscape  just  what  it  meant  to  hmi  in  the  light  of  his 
knoAvledge,  needs,  and  tendencies  of  the  moment. 

All  interpretation  is  partial.  It  is  confined  to  the 
limits  of  the  sense-organs,  the  time,  opportunity,  and 
inclination  for  detailed  scrutiny,  habits  of  inference,  the 
purpose  in  mind,  the  store  of  knowledge  about  it,  etc. 
These  facts  are  so  universal  that  we  scarcely  take 
cognizance  of  them.  Before  the  psychologist  was  in- 
terested in  the  doctrine  of  apperception,  schoolboys  de- 
lighted in  reciting  the  happy  story  of  the  six  blind  men 
of  Indostan  who  went  to  see  the  elephant.  The  es- 
sential lines  suffice  for  quotation : 


First  blind  man,  falling  against  the  elephant's  side: 
"God  bless  me!   but  this  elephant 
Is  very  like  a  wall." 

Second  blind  man,  feeling  the  tusk: 

"This  wonder  of  an  elephant 
Is  very  like  a  spear." 

Third  blind  man,  grasping  the  squirming  trunk: 
"I  see",  quoth  he,  "the  elephant 
Is  very  like  a  snake." 

The  fourth  blind  man,  clasping  the  knee: 

"  'Tis  clear  enough,  the  elephant 
Is  very  like  a  tree." 

The  fifth  blind  man,  catching  the  ear: 

"This  marvel  of  an  elephant 
Is  very  like  a  fan." 


148  APPERCEPTION 

The  sixth,  seizing  the  swinging  tail : 

"I  see",  quoth  he,  "the  elephant 
Is  very  like  a  rope." 

"And  so  these  men  of  Indostan 
Disputed  loud  and  long, 
Each  in  his  own  opinion 
Exceeding  stiff  and  strong. 
Though  each  was  partly  in  the  right, 
And  all  were  in  the  wrong." 

The  interpretation  is  personal ;  it  is  an  act  for  itself. 
We  can  never  fully  perceive  anything  without  falling 
into  a  cluster  of  associations  which  are  peculiar  to  our- 
selves. How  does  the  salad  taste  ?  That  depends  upon 
the  season,  how  much  one  has  eaten,  one's  preference 
for  certain  dressing,  the  stage  of  dyspepsia,  and  the 
attitude  toward  the  hostess  and  the  cook.  What  do  you 
see  in  this  picture  ?  The  reflection  of  something  in 
yourself.  It  is  a  happy  freak  of  nature  that  so  many 
men  sincerely  marry  the  ''best  woman  on  earth,"  and 
that  their  children  are  the  most  wonderful  children  in 
the  community. 

Our  normal  interpretation  is  always  purposive.  As 
a  rule,  we  attend  to  sense  impressions  only  in  such  a 
manner  as  to  get  the  needed  meaning  out  of  them.  We 
instinctively  do  this  in  the  most  economic  way.  As  we 
grow  in  experience  we  can  get  along  with  less  and  less  of 
the  outward  impression,  the  sensory  cue.  A  good 
reader  will  easily  see  only  the  significant  words  on  a 
page ;  prepositions,  articles,  and  adverbs  are  often  sup- 
plied from  the  context.  When  we  discover  that  it  is 
John  Smith  who  is  approaching,  we  have  attained  to 
certain  marks  of  identification  which  suffice  to  give  us 
the  desired  information.     It  may  be  that  we  have  seen 


APPERCEPTION  149 

his  beard,  his  profile,  the  swagger  of  his  walk,  his 
sombrero  hat,  or  merely  a  vague  something  in  the  place 
which  we  knew  Mr.  Smith  to  be ;  we  may  have  heard  his 
greeting,  or  only  the  sound  of  his  footsteps.  When  we 
see  a  horse  we  do  not  ordinarily  examine  if  it  has  four 
legs.  Many  intelligent  persons  do  not  know  how  many 
legs  a  fly  has,  although  they  have  observed  flies  with 
decided  interest,  from  the  point  of  view  of  comfort,  a 
thousand  times. 

Perception  is  of  "^definite  and  probable  things.''  The 
sound  of  the  approaching  footsteps  comes  out  from  the 
chaos  of  noises  around  and  becomes  something  definite. 

Furthermore,  pictorial  representations  to  the  eye  are 
"mere  suggestions."  An  artist  can  draw  a  human  face, 
full  of  expression,  with  half  a  dozen  lines.  The  speedy 
crayon  artist  can  delight  his  audience  with  character 
sketches  that  remind  one  of  moving  pictures.  The 
depth,  the  distance,  the  relief,  the  solidity,  and  the  size 
in  a  drawing  have  hardly  any  correspondence  to  real 
life.  Drawung  is  an  exceedingly  abbreviated  code  of 
signals  to  the  eye.  Hence  we  have  formed  a  habit  of 
approaching  all  graphic  representations  with  a  generous 
constructive  imagination. 

2.  Bias. — Eecord  what  Fig.  20  represents  to  you,  and 
observe  the  operation  of  the  principles  mentioned  in 
Exp.  1. 

Which  of  the  two  possible  views  shall  present  itself 
first  depends  largely  upon  wdiich  side  of  the  figure  one 
attempts  to  read  meaning  into.  The  face  is  of  greater 
significance  than  the  back  of  the  head.     One  person 


150  APPEECEPTION 

sees  a  rabbit,  another  sees  a  duck.  Fortunately  in  this 
case  one  can  accept  the  view  of  the  other  when  it  is 
pointed  out. 

The  thing  to  be  emphasized  is  that  when  the  object  is 
a  rabbit  it  is  a  rabbit,  and  when  it  is  a  duck  it  is  a  duck. 
Yet  here  the  object  consists  in  a  rigid  and  clear  figure  on 
the  paper.  Xow,  when  the  objective  marks  are  not  so 
rigid,  as  in  vague  sensations,  indistinct  images,  partial 
generalization;  and  when  the  interpretation  is  an  ex- 
pression of  feeling  or  the  realization  of  a  longing,  what 
an  enormous  range  in  the  possibilities  of  interpretation 


Fig.  20.     (After  Jastrow.) 
is  opened !     There  is  abundant  opportunity  for  bias, 
prejudice,  and  old-fogy  ism. 

Regarding  the  kaleidoscopic  appearances  under  the 
microscope  when  new  features  are  under  discussion,  one 
says  rabbit  and  another  says  duck.  In  giving  testimony 
on  the  incidents  of  a  wreck,  one  witness  maintains  rab- 
bit and  another  maintains  duck.  Is  the  world  going- to 
the  dogs?  One  ssijs  rabbit,  another  says  duck.  Con- 
sidering the  beauty  of  a  painting,  one  says  rabbit,  an- 
other says  duck.  Considering  the  future  life,  one  says 
rabbit,  another  says  duck. 

Like  the  blind  men  of  Indostan,  each  can  remain 


APPERCEPTION  151 

sincere,  honest,  and  unshaken  in  his  convictions  because 
he  is  satisfied  with  the  view  he  has  obtained  and  does 
not  give  the  other  side  an  opportunity  to  develop.  One 
approaches  his  object  with  the  expectation  of  rabbit, 
another  with  the  expectation  of  duck.  This  expecta- 
tion can  in  turn  be  traced  to  environment,  temperament, 
training,  desire,  etc.  Bias  is  the  satisfaction  with  a 
partial  view.  Our  experiment  contains  a  simple  and 
rigid  illustration.  The  more  complex  the  situation  is, 
the  more  danger  there  is  of  warp,  twist,  prepossession, 

o  o  o  o  o 

o  o  o  o  o 

o  o  o  o  o 

o  o  o  o  o 

o  o  o  o  o 

Fig.  21. 

bigotry,    quirk,    crotchet,    whim,    and   other   forms    of 
obliquity  which  may  result  from  falling  into  a  rut. 

To  become  educated  is  to  acquire  the  ability  to  put 
oneself  into  the  place  of  another. 

3.  Subjective  Grouping. — The  circles  in  Fig.  21  are 
all  alike  and  they  are  grouped  symmetrically.  Group 
them  subjectively  by  voluntary  attention  in  turn  as  fol- 


152 


APPEKCEPTION 


lows:  (1)  five  horizontal  lines,  (2)  five  vertical  lines, 
(3)  two  diagonal  lines,  and  (4)  an  outside  large  square 
wdth  an  inside  small  square  and  a  circle  in  the  center. 
Record  how  these  subjective  gi'oupings  affect  the  ap- 
parent size,  clearness,  and  spacing  of  the  circles. 

This  experiment  further  emphasizes  the  fact  that  the 
actual  physical  object  seems  to  change  as  Ave  ascribe 
different  meanings  to  it.  This  figure  in  its  plainness 
and  rigidity  puts  the  principle  to  a  most  critical  test. 
The  subjective  grouping  unquestionably  changes  the  ap- 
parent spacing,  clearness,  and  size  of  the  circles. 

The  same  principle  is  illustrated  in  Fig.  22.  Xow  it 
is  a  star ;  now  it  is  a  polygon  with  accessory  points ;  now 


Fig.  22. 

it  is  a  figure  with  two  sides  parallel  and  ends  feathered. 
In  each  case  the  lines  on  the  page  look  different. 

4.  Reversible  Perspective,  a.  The  Reversal — Look 
for  a  few  moments  at  Figs.  23,  24,  and  25  in  turn 
and  observe  that  these  figures  are  unstable;  they  are 
seen  clearly  and  satisfactorily  in  a  given  aspect  at  one 
moment,  but  all  at  once  they  suddenly  lop  over  and 


APPERCEPTION 


153 


present  a  radically  different  relief."^     Record  the  num- 
ber of  blocks  in  Fig.  24. 

This  experiment  is  introduced  in  order  to  illustrate 
how  it  is  possible  to  take  a  given  case  of  apperception 
and  trace  it  to  underlying  fundamental  motives.  There 
is  a  reason  for  every  actual  apperception  of  an  object  or 
event,  no  matter  how  bizarre   it  may  be.     It  is  the 


Fig.  24. 

business  of  psychology  to  trace  such  motives  in  order  to 
explain  mental  life. 

These  figures  are  not  drawn  in  true  relief;  they  are 
made  ambiguous  so  that  either  of  two  radically  dif- 
ferent views  may  appear.     Why   should  they  not  be 

*  Looking  at  figures  with  one  eye  favors  the  reversal ;  so  does 
also  holding  the  figure  at  a  distance. 


154  APPERCEPTION 

seen  as  they  really  are — plane  figures  on  the  surface  of 
the  page  ?  The  answer  is  to  be  found  in  a  tendency 
whose  history  can  be  traced.  Nearly  all  objects  in  which 
we  are  interested  have  volume  and  relief;  relief  can 
be  only  suggested  in  a  drawing;  hence  we  have  formed 
deep-rooted  habits  of  interpreting  objects  as  having  re- 
lief, no  matter  how  imperfect  the  device  for  represent- 
ing it  in  the  drawing. 

Here  again  it  is  significant  that  when  one  particular 
view  is  obtained  it  is  entirely  adequate;  there  is  no 


Fig.  25.    (After  Walliu.) 

ambiguity  in  the  experience.  Indeed,  some  observers 
find  difficulty  in  obtaining  any  reversal.  Yet,  presto! 
there  is  an  instantaneous  and  complete  reorganization  of 
the  figure  right  under  the  eye,  as  if  by  some  magic 
wand.  As  soon  as  the  reversal  has  once  taken  place,  the 
figure  continues  to  oscillate  irresistibly.  The  reason 
it  may  not  have  reversed  soon  after  the  first  trial  is  that 
the  observer  did  not  know  what  to  expect  to  see.     Now 


APPEKCEPTION  155 

that  the  two  views  have  been  seen  and  are  equally  clear 
and  convincing,  expectant  attention  favors  the  change. 

h.  The  Normal  Bate  of  Fluctuation. — Call  the  first 
relief  that  appears  ''One"  and  the  second  "Two."  Let 
O  look  continuously  at  Fig.  23  and  call  out  "One"  or 
"Two"  as  the  respective  changes  take  place.  Start 
when  the  second-hand  of  your  watch  is  at  60  and  record 
the  position  of  the  hand  at  each  signal  for  two  minutes. 
Record  the  approximate  duration  of  each  relief  in  the 
successive  appearances.^  Observe  Figs.  24  and  25  in 
the  same  manner. 

The  observer  has  now^  completely  overcome  his  bias. 
He  has  been  liberated  from  the  attitude  in  which  he 
asserted  that  there  were  only  six  blocks  and  now  takes  a 
more  generous  and  enlightened  view  of  the  situation. 
He  now  realizes  that  there  are  greater  resources  in  the 
figures  than  he  had  first  credited  them  Avith,  and  per- 
haps draws  a  sweeping  moral  as  to  the  operation  of  the 
same  principles  in  his  ordinary  interpretation  of  people, 
events,  theories,  ideals,  etc.  After  one  has  once  grasped 
the  truth,  it  will  not  down,  but  lights  the  way  for  further 
penetration. 

c.  The  Fastest  Rate  of  Fluctuation. — Proceed  with 
Fig.  23  as  in  Exp.  4  h,  but  let  O  force  the  rate  of  change 
as  much  as  possible.  Record  the  number  of  changes 
and  O's  introspection  of  the  effort  to  force  the  rate. 

d.  The  Sloicest  Rate  of  Fluctuation. — Proceed  as  in 
Exp.  4  c,  but  let  O  struggle  to  maintain  the  figure  in  a 
stable  view. 


*  If  no  reversal  takes  place  in  the  two  minutes,  it  is  because 
0  did  not  get  sufficiently  familiar  with  the  two  views  in  Exp.  4  a. 


156 


APPERCEPTION 


The  results  differ  with  ingenuity  and  chance  clues  of 
the  observer.  For  some  the  effect  of  the  effort  is  to  in- 
crease the  rate  of  the  fluctuation  in  both  experiments ; 
for  others  there  may  be  some  appreciable  success  both  in 
the  increase  and  the  decrease  of  the  rate ;  still  others 
may  discover  the  secret  of  the  reversal  and  be  able  to 
hold  or  reverse  at  pleasure.  What  this  secret  is  we  shall 
discover  in  the  next  experiment. 

e.  Control  of  the  Reversal. — Observe  that  Fig.  26 
may  appear  to  represent  a  glass  jar  one  moment  a&  seen 


from  above,  and  another  as  seen  from  below. 
Fixate  the  eyes  in  successive  trials,  upon  the  points  in 
the  edges  marked  A,  B,  R,  and  8  respectively,  and  ob- 
serve that  the  figure  remains  stable  so  long  as  you  retain 
a  steady  fixation  of  one  of  these  points,  and  that  the 
relief  is  always  the  same  for  a  given  point.  Record  for 
each  point  whether  the  top  or  the  bottom  view  prevails. 
The  secret  then  lies  in  allow^ing  a  certain  point  in 
the  figure  to  catch  and  hold  the  eye.  Fig.  26  is  favor- 
able for  the  demonstration  of  this  because  it  is  large 


APPERCEPTION  157 

and  simple  enough  to  enable  one  to  control  the  regard. 
It  is  difficult  to  verify  this  principle  on  the  smaller 
figures  which  have  finer  patterns  over  which  the  eye 
involuntarily  wanders  from  one  point  of  regard  to 
another. 

The  general  law  observed  is  that  the  point  which  first 
catches  the  eye  or  tends  to  hold  its  regard  is  perceived 
as  a  near  j^art  of  the  object.     This  fixes  the  view. 

Why  should  the  part  which  first  catches  the  eye  be 
judged  near  ?  It  is  a  habit.  Whenever  we  look  at 
objects,  economy  bids  us  look  first  at  the  near  side,  other 
things  being  equal ;  this  has  resulted  in  the  tendency  of 
assuming  that  the  first  part  seen  is  the  near  part  of  the 
object. 

Why  should  the  point  upon  which  we  maintain  regard 
be  judged  near?  It  is  a  habit.  Whenever  we  try  to 
see  a  whole  complex  object  there  is  a  tendency  to  ac- 
commodate for  a  point  near  the  center  of  the  surface, 
and  this  is,  as  a  rule,  near  us;  the  uniformity  of  this 
experience  has  resulted  in  the  tendency  of  assuming 
that  when  we  regard  a  fairly  central  point  in  a  complex 
figure,  this  point  is  a  near  part  of  the  object. 


CHAPTER  XIII 

ATTENTION 

For  Tioo* 

In  reading  this  paragraph  your  attention  moves 
from  word  to  word,  following  close  npon  the  movement 
of  the  point  of  regard,  and  you  are  probably  aw^are  of 
this  movement  of  attention  as  an  expression  of  personal 
activity,  as  an  advancing  wave  in  the  tide  of  your  feel- 
ing of  interest,  and  as  a  complex  of  sensory  impressions 
of  bodily  condition  and  processes  of  adjustment.  These 
are  the  most  direct  ways  in  which  w^e  become  aware  of 
it;  but  attention  is  not  an  activity  in  itself,  it  is  not 
essentially  a  feeling  of  interest,  nor  is  it  essentially 
awareness  of  the  processes  of  bodily  accommodation. 
Attention  is  the  focus  of  consciousness  as  a  w^hole,  the 
state  or  form  of  concentration  of  the  seeing,  thinking, 
remembering,  feeling,  doing,  etc.,  at  a  given  moment. 
Attention  is  to  consciousness  as  the  point  of  regard  is  to 
the  field  of  vision,  the  focal  point. 

1.  Rhythm  of  Attention. — When  O  is  seated  with 
eyes  closed,  in  a  quiet  room,  hold  an  open  watch  at  such 
a  distance  from  his  ear  that  he  can  barely  hear  it.  At 
a   signal   let   him   direct   his   attention   as   steadily   as 

*  This  experiment  must  be  performed  in  comparative  quiet, 
which  is  usually  best  obtained  in  the  evening. 

158 


ATTENTION  159 

possible  upon  the  hearing  of  the  sound  for  one  minute 
and,  with  a  pencil  in  hand,  point  upward  when  he  hears 
the  sound  and  downward  when  he  does  not  hear  it.^ 
Following  the  second-hand  on  the  watch,  tap  time 
quietly  in  the  note-book,  making  a  dotted  line,  thus, 

,  one  dot  per  second ;  adopt  tw^o  levels  and  trace 

on  the  upper  when  O  points  upward,  and  on  the  lower 
wdien  he  points  downward,  like  this, 

Preserve  and  nmnber  the  curves  as  permanent 
records.  Make  a  table  showing  the  number  of  periods 
and  the  length  of  each  period  in  seconds  (a)  for  ''Sound 
heard"  and  (h)  for  ''Sound  not  heard.''  Make  five 
trials. 

This  experiment  demonstrates  that  attention  fluc- 
tuates and  is  periodic.  For  reasons  of  biological 
economy,  consciousness  cannot  remain  focused  upon  a 
single  unchanging  object  for  more  than  a  moment  at  a 
time ;  the  focus,  i.e.,  the  attention,  is  intermittent. 

A  liminal  stimulus  was  chosen  because  it  is  easier  to 
observe  the  changes  in  that  than  in  strong  stimuli, 
although  the  principle  of  fluctuation  applies  to  both,  in- 
deed perhaps  to  all  objects  of  consciousness.  And  the 
sense  of  hearing  was  chosen  because  the  stimulus  can 
be  most   satisfactorily   controlled   for   that   sense.     In 

*  If  the  fluctuation  does  not  occur,  the  watch  is  either  too 
near  or  too  far  away;  find  such  a  distance  that  it  will  be  heard 
about  half  of  the  time. 

A  common  source  of  failure  in  a  beginner  is  that  he  expects 
to  hear  the  tick  at  one  moment  as  well  as  at  another  and  there- 
fore fails  to  observe  that  he  does  not  actually  hear  it  but  merely 
imagines  that  he  hears  it  part  of  the  time.  An  attentive  ob- 
server may  be  able  to  record  the  missing  of  a  single  tick  or  two. 

If  any  wave  in  a  curve  is  due  to  outside  disturbance,  discard 
that  record  and  try  it  over  again. 


160 


ATTENTION 


sight,  toucli,  and  smell  the  test  is  complicated  by  the 
rapid  changes  of  adaptation  and  fatigue.  The  most 
satisfactory  stimulus  is  a  constant  tone  of  medium  pitch. 
The  waves  of  attention  are  not  smooth.  If  we  could 
get  a  detailed  record  of  attention  to  a  constant  stimulus 
such  as  a  sustained  tone,  a  gray  surface,  or  a  uniform 
pressure,  it  would  probably  take  a  form  something  like 
the  white  surface  in  Fig.  27,  which  might  represent  the 
distribution  of  attention  for  about  ten  seconds  schemat- 


FiG.  27. 

ically.*     Both  crests  and  troughs  are  rugged.     In  the 

case  of  a  tone,  for  example,  the  result  of  a  very  faint 

tone  might  be  represented  at  the  level  a-a\  where  the 

tone  is  heard  very  faintly  and  only  for  a  relatively^  short 

period;   the   result  for  a   stronger   stimulus  might  be 

represented  at  the  level  h-h',  where  the  tone  is  clearer 

and  stronger  and  the  periods  of  duration  are  relatively 

longer ;  while  the  result  for  a  strong  stimulus  might  be 

represented  at  the  level  c-c',  which  indicates  that  the 

observer  has  the  impression  of  being  aware  of  the  tone 

*  For  attention  this  is  merely  a  hypothetical  diagram ;  actually 
it  is  a  photograph  of  the  manometric  tlame  for  a  vowel. 


ATTENTION  161 

all  the  time  but  that  there  is  a  rhythmic  fluctuation  in 
its  clearness  and  strength."^ 

Probably  all  mental  activity — sensation,  discrimina- 
tion, feeling,  memory,  will,  etc. — is  rhythmic.  The  two 
waves  in  Fig.  27  are  made  up  of  smaller  waves,  and 
these  in  turn  of  still  smaller  ones.  Measurements  on 
long  periods  of  attention  show  that  there  may  be  waves 
as  long  as  an  hour ;  smaller  waves,  reckoned  in  minutes, 
may  be  traced  inside  of  these ;  and  within  the  ' 'minute- 
waves"  we  find  the  so-called  ''second-waves."  Our  con- 
ception of  the  flow  of  attention,  or  the  fluctuation  in  the 
capacity  for  a  certain  conscious  activity,  is  then  this: 
There  are  inflnitely  short  ripplets  of  attention,  hardly 
perceptible ;  these  form  the  surface  of  ripples,  which  in 
turn  form  the  surface  of  wavelets ;  and  these  wavelets  in 
turn  form  the  surface  of  waves,  and  so  on.  Thus,  all 
attention  is  rhythmic,  and  there  is  rhythm  within 
rhythm  from  the  infinitesimally  short  to  the  very  long, 
even  daily  and  annual  periodicities. 

The  length  of  the  attention-wave  (second-wave) 
varies  with  numerous  conditions,  such  as  kind  and 
strength  of  stimulus,  practice,  temperament,  psycho- 
physical condition,  effort,  etc.  The  shortest  fluctua- 
tions are  probably  too  rapid  to  be  detected,  and  ordi- 
narily a  single  crest  of  attention  cannot  be  maintained 
for  more  than  ten  or  twelve  seconds.     For  conditions 


*  It  is  evident  that  the  ratio  of  the  length  of  the  crests  to  the 
length  of  the  troughs  in  the  above  experiment  depended  upon 
the  strength  of  the  stimulus  adopted.  When  a  stimulus  is  com- 
paratively weak  the  troughs  are  long  and  the  crests  short; 
whereas  the  order  is  reversed  when  the  stimulus  is  comparatively 
strong. 


162  ATTENTION 

like  those  of  the  present  experiment  an  average  of  from 
six  to  eight  seconds  for  a  complete  wave  is  about  normal. 
The  periodicity  has  come  into  existence  because  it  is 
effective,  economic,  and  agreeable.*  To  illustrate  these 
three  features,  let  us  aid  our  constructive  imagination 
by  Fig.  28.  The  vertical  bar  represents  something  that 
we  can  be  conscious  of,  e.g.,  a  tone  which  is  not  heard 
because  not  attended  to,  and  that,  as  we  turn  to  listen 
to  it,  our  attention  may  flow  in  any  one  of  the  forms 
ttj  h,  or  c,  which  represent  surfaces  of  equal  magnitude. 
Now  if  it  takes  the  form  a,  the  object  will  be  in  con- 


FiG.  28. 
sciousness  continuously,  but  only  in  small  part;  if  it 
takes  the  form  c,  the  object  will  be  comprehended  com- 
pletely as  it  passes  through  consciousness ;  h  represents 
a  mean  between  these  two  extremes.  As  nothing  would 
be  gained  by  holding  the  tone  in  consciousness  longer 
than  c  does,  c  is  the  most  effective  form. 

Then,  c  gives  consciousness  a  period  of  rest  propor- 
tional in  length  to  the  degTee  of  concentration.  As  c 
accomplishes  four  times  as  effective  work  as  a  with  a 
given  quantity  of  energy  and  still  allows  a  good  period 
of  complete  rest  before  the  next  wave,  it  follows  that  c 
represents  the  most  economic  form  of  expenditure. 

*  The  old  philosophers  had  a  sort  of  poetic  dream  that  all 
nature  is  rhythmical;  and  the  more  we  discover  of  nature's 
ways  the  more  we  see  of  periodicity.  Electricity  furnishes  a 
good  example:  the  alternating  current  is  far  more  effective  and 
economic  than  the  direct. 


ATTENTION  163 

When,  as  in  this  case,  the  object  of  consciousness  is 
constant,  when  it  can  be  divided  into  natural  groups  by 
attention  itself,  or  when  the  object  is  itself  periodic, 
as  in  music,  poetry,  or  rhythmic  movements,  the  atten- 
tion-waves adapt  themselves  to  the  rhythm  so  that  the 
essentials  of  the  group  are  grasped  during  the  crest  of 
the  attention-wave  and  each  momentary  effort  is  well 
timed  and  is  followed  by  a  period  of  rest.  Applying 
this,  then,  to  the  three  wave-forms  in  the  figure,  we  see 
that  as  c  affords  the  greatest  feeling  of  ease  and  com- 
pleteness in  the  grasp,  permits  rest,  and  tends  to  make 
the  process  automatic,  it  is  the  most  agreeable.* 

The  psychological  explanation  for  our  enjoyment  of 
rhythm  in  all  sorts  of  mental  activity  is  to  be  found 
largely  in  this  basal  fact  of  a  natural,  biological  rhythm 
of  attention. 

What  are  the  immediate  psychophysical  causes  and 
conditions  of  these  wave-forms  ?  Numerous  investi- 
gators are  at  work  on  that  problem  at  the  present  time, 
but  it  is  too  early  to  draw  any  general  conclusion,  and 
details  would  take  us  too  far  into  technicalities.  It  is 
probable  that  we  shall  be  able  to  trace  the  waves  into 
their  constituent  elements,  both  central  and  peripheral. 

Language  forces  us  to  use  terms  which  might  signify 

the  adoption  of  one  or  another  of  the  extreme  theories 

of  attention.     This  should  not  mislead  us  into  thinking 

that  we  know  what  the  ultimate  nature  of  consciousness 

or  attention  is. 

*  There  is  an  analogy  in  the  learning  of  a  game.  The  beginner 
is  conscious  of  every  step  in  the  process  and  usually  fails; 
whereas  the  expert  times  his  effort  and  uses  it  only  at  crucial 
points.  The  secret  of  the  Japanese  wrestling  feat  jiu-jitsu  lies 
in  the  instantaneity  of  the  act. 


164  ATTENTION 

2.  Division  of  Attention. — Time  O  for  thirty  seconds 
and  let  him  count  aloud  as  fast  as  he  can  from  one  np 
and  at  the  same  time  write  numbers  in  an  independent 
series  as  fast  as  he  can  from  one  np ;  thus,  1,  2, 
3,  etc.  Kote  errors  made  in  the  counting.  Let  O 
record  the  number  reached  in  counting  and  writing 
respectively,  the  errors  noted  in  counting  and  in  writ- 
ing, and  any  influence  of  one  series  upon  the  other  that 
he  can  remember  or  observe.     Make  five  trials. 

The  observer  failed  in  the  effort  to  divide  attention 
and  direct  it  upon  both  processes  at  the  same  time.  He 
noticed  an  irresistible  tendency  to  allow  the  attention  to 
oscillate  from  one  process  to  the  other.  In  so  far  as 
the  two  processes  actually  went  on  simultaneously,  one 
was  automatic,  i.e.,  went  on  without  attention.  Among 
the  conspicuous  errors  are  probably  speaking  a  number 
due  in  writing,  writing  a  number  due  in  speaking,  and 
partial  combination  of  a  number  in  one  series  with  a 
number  in  the  other. 

Strictly  we  can  attend  to  only  one  process  at  a  time. 
When  two  or  more  mental  processes  are  supposed  to  be 
carried  on  simultaneously,  either  the  attention  oscillates 
so  rapidly  from  one  to  the  other  that  they  seem  simul- 
taneous, or  all  but  one  of  the  processes  are  automatic. 
Usually  these  two  principles  cooperate.* 

*  James  quotes  Paullian:  "I  multiply  421,312,212  by  2;  the 
operation  takes  six  seconds;  the  recitation  of  four  verses  also 
takes  six  seconds.  But  the  two  operations  done  at  once  take 
only  six  seconds,  so  that  there  is  no  loss  of  time  from  combining 
them."  Here  the  reciting  must  have  been  entirely  automatic  and 
habitual  in  connection  with  the  multiplying.  We  should  not 
think  that  the  reciting  required  more  attention  than  ordinary, 
unchecked,  happy  whistling  would. 


ATTENTION  165 

Still  we  must  remember  that  attention  is  a  matter  of 
degree  of  concentration.  I  may  see  the  whole  land- 
scape before  me,  but  see  nothing  in  particular.  The 
process  upon  which  attention  is  actually  directed  is  in 
the  focus  of  consciousness,  while  the  other  processes 
must  be  more  or  less  out  of  focus,  if  consciousness  is 
focused  at  all.  All  that  we  do  skillfully  and  nearly  all 
that  we  do  well  is  done  without  much  attention. 
Several  such  processes  can  go  on  simultaneously  to  ad- 
vantage because  they  are  more  or  less  automatic  and 
demand  attention  only  at  crucial  points  which  attention 
can  reach  in  its  oscillations.  In  the  development  of 
habit  such  points  are  reduced  to  a  minimum.^ 

3.  The  Scope  of  Attention. — Lay  a  sheet  of  paper 
on  the  table  and  tap  at  a  uniform  rate  with  the  point  of 
a  pencil  as  rapidly  as  you  can  on  the  sheet.  Make  from 
three  to  twelve  taps,  and  require  O  to  say,  without 
counting  them,  how  many  taps  he  heard.  Record  O's 
estimate  and  the  true  number  as  shown  by  the  num- 
ber of  dots  on  the  paper.  Make  ten  trials.  Before 
showing  the  results  to  O  record  his  statement  of  how 
many  taps  he  feels  sure  that  he  can  estimate  correctly 
within  a  single  span  of  attention  like  this. 

The  above  test,  though  crude,  serves  to  illustrate  the 
principle  that  the  range,  scope,  or  span  of  attention  is 
limited.     The  observer's  estimate  was  probably  correct 

*  In  transcribing  rough  notes  into  a  finished  paragraph  on 
the  typewriter,  reading,  thinking,  and  fingering  are  three  proc- 
esses which  run  parallel,  thereby  favoring  oscillation  of  attention 
where  necessary.  Yet  the  best  work  is  done  when  the  writer  is 
oblivious  of  notes  or  fingering  and  is  completely  absorbed  in  the 
flow  of  the  thought. 


166  ATTENTION 

up  to  about  five  taps,  but  when  a  group  had  more  than 
that  number  of  taps  the  estimate  was  more  or  less  of  a 
guess  on  the  ''mass." 

The  experiment  is  usually  performed  as  a  sight  test 
with  elaborate  apparatus.  Letters,  numerals,  dots, 
lines,  etc.,  are  shown  in  groups  in  exposures  which  are 
so  short  as  to  prevent  eye-movement.  In  a  0.05-second 
exposure  one  can  normally  grasp  with  certainty  from 
three  to  six  similar  and  simple  objects,  such  as  letters. 
If  the  objects  are  psychologically  more  complex,  fewer 
are  grasped.  If  the  simple  objects  are  united  into  larger 
units,  e.g.,  the  letters  are  united  into  short  words,  one 
can  grasp  almost  as  many  of  the  larger  units,  provided 
they  are  familiar;  one  can  grasp  about  three  times  as 
many  letters  when  they  form  words  as  when  they  do  not 
form  words.  It  is  about  as  easy  to  grasp  one's  full 
name  as  to  grasp  the  initials.  In  short,  the  span  de- 
pends upon  the  coherence  of  the  elements  which  are 
grasped  together. ^ 

Interest  and  practice  are  the  main  sources  of  strong 
grasp   of   attention.       The   artist   perceives   the   color 


*  The  capacity  for  grasping  facts  by  large  units  increases  with 
mental  development.  Take  the  case  of  writing:  the  child  first 
begins  on  the  penmanship  stage  and  is  conscious  of  "position" 
and  parts  of  letters;  he  then  passes  to  the  spelling  stage  and  is 
conscious  of  letters  as  the  elements  of  words;  later  he  enters 
the  grammar  stage  and  is  conscious  of  words  in  the  construction 
of  the  sentence;  this  leads  to  the  rhetoric  stage,  in  which  he  is 
conscious  of  the  construction  of  the  paragraph  from  phrases, 
clauses,  and  sentences;  and  finallj^,  if  he  really  becomes  an 
effective  writer,  ho  reaches  the  logical  stage  and  the  writing  is 
grasped  in  terms  of  ideas  which  take  the  form  of  paragraphs. 
As  he  reaches  each  higher  stage,  the  units  of  the  lower  stage  must 
more  or  less  "take  care  of  themselves".  Few  adults  reach  the 
highest  level. 


ATTENTION  167 

scheme  of  a  painting  at  a  glance ;  and  many  a  woman 
sees  intricate  details  in  a  rival's  toilette  in  but  a 
moment's  observation. 

4.  Intensifying  Effect  of  Attention. — Suspend  two 
watches,  one  to  the  right  and  the  other  to  the  left  of  the 
head,  at  such  distances  that  each  can  be  just  distinctly 
heard.  With  eyes  closed,  direct  your  attention  alter- 
nately to  one  and  the  other  and  observe  whether  the 
tick  seems  louder  in  the  one  to  which  you  attend. 

The  sensation  to  which  the  attention  is  directed 
probably  becomes  stronger.  If  we  strike  a  chord  on  the 
piano  and  hold  the  keys  down  while  the  tones  ring  off, 
"it  is  possible,  by  successive  attentions,  to  construct  a 
melody  from  the  separate  tones,  while  the  whole  chord 
sounds  on  as  an  accompaniment"  (Titchener).  Some 
psychologists  think  that  the  same  may  be  illustrated  in 
weak  sensations  in  other  senses,  e.g.,  color  and  touch.* 
But  this  intensifying  effect  is  limited  to  comparatively 
weak  stimuli.  Strong  tones,  colors,  and  pressures  are 
not  intensified  by  attention.  An  overtone,  but  not  its 
fundamental,  is  intensified  by  attention. 

In  a  similar  manner  attention  increases  the  apparent 
duration  of  comparatively  short  mental  processes. 

A  further  closely  related  characteristic  of  the  process 
attended  to  is  that  it  seems  to  precede  other  processes 
which  occur  simultaneously  with  it  but  are  not  attended 

*  This  is  the  principal  element  in  the  explanation  of  "the  feeling 
of  being  stared  at".  Many  persons  report  distinct  experiences 
of  feeling  that  a  person  somewhere  behind  is  staring  at  them; 
they  are  conscious  of  prominent  tactual  sensations  in  the  neck. 
These  sensations  are  normally  always  present  if  attended  to;  the 
expectant  attention  intensifies  them. 


168  ATTENTION 

to.  The  usual  form  of  the  experiment  illustrative 
of  this  law  is  to  present  simultaneously  two 
stimuli  while  the  observer  notes  that  according  to  the 
direction  of  the  attention,  he  can  make  the  one  or  the 
other  appear  to  come  first.  One  can  make  either  the 
bell-stroke  or  the  click  of  the  metronome  arise  first, 
although  in  a  good  instrument  they  really  sound  at  the 
same  instant. 

This  explains  a  celebrated  experiment  which  proves 
that  we  cannot  attend  to  auditory  and  visual  stimuli  at 
the  same  time.  The  experiment  is  an  imitation  of  the 
recording  of  the  transit  of  a  star  by  an  astronomer.  A 
sound  and  a  visual  impression  occur  together,  but  the 
observer  invariably  records  one  as  having  occurred  be- 
fore the  other.  What  the  order  shall  be  is  determined 
by  the  type  of  imagery  the  observer  represents.* 

5.  Clearness  and  Detail. — Look  at  Fig.  29  and 
answer  the  question.  Observe  the  apparent  changes 
in  the  lines  of  the  figure  the  moment  you  solve  the 
puzzle. 

Attention  makes  the  image  of  an  object  clearer  and 
more  meaningful.  This  is  the  most  striking  and 
fundamental  characteristic  of  attention.  Fig.  29  is 
usually  seen  first  as  a  disagreeable  face  and  then  as 


*  About  a  hundred  years  ago  two  astronomers  who  compared 
notes  found  that  there  was  a  large  constant  difference  in  their 
observations  on  the  transit.  Investigation  revealed  the  fact  that 
one  of  them  was  a  visualizer  and  the  other  an  audile;  one  at- 
tended first  to  the  visual  impression  and  the  other  attended  first 
to  the  auditory  impression.  The  difference  between  the  observa- 
tions of  the  two  astronomers  was  alwaj's  the  algebraic  sum  of  their 
errors.  This  discovery  marks  the  beginning  of  the  study  of  the 
so-called  "personal  equation". 


ATTENTION 


169 


something  entirely  different,  agreeable,  and  clear.  The 
details  which  are  clear  and  dominant  when  we  apper- 
ceive  one  view  tend  to  vanish  in  the  background  when 
we  apperceive  the  other. 

It  is,  however,  important  to  make  a  distinction  be- 
tween clearness  and  intensity.     Faint  stimuli  become 


Fig.  29. 


both  more  intense  and  clear,  while  medium  and  strong 
stimuli,  as  a  rule,  gain  only  clearness  through  attention. 


6.  Distraction    of    Attention:    Mind- Wandering. — 

Select  fifteen  consecutive  lines  from  a  paragraph  and 
count  how  many  a's  there  are  in  the  selection.  Count 
as  fast  and  accurately  as  possible  and  apply  yourself  to 
the  task  as  exclusively  as  possible.     Immediately  after 


170  ATTENTION 

the  counting,  retrace  the  selection  and  write  out  a  full, 
frank,  and  specific  account  of  the  irrelevant  impressions, 
memories,  thoughts,  feelings,  and  impulses  which  came 
more  or  less  into  the  focus  of  attention  against  your  best 
effort. 

Unwavering  attention  is  a  fiction.  There  are  great 
individual  differences  in  the  power  of  application  of  at- 
tention, but  no  mentally  alert  student  can  apply  himself 
so  closely  even  to  this  simple  task  but  that  he  will  have 
a  long  and  intricate  list  of  mind-wanderings  to  report. 
Indeed,  the  mind  wanders  so  much  for  all  persons  that 
a  scant  report  in  this  experiment  would  be  indicative  of 
lack  of  power  of  observation  rather  than  a  high  degree 
of  concentration.  Like  many  other  processes,  such  as 
after-images,  double  images,  etc.,  which  ordinarily  are 
not  desirable,  these  mind-wanderings  are  not  easy  to 
trace  without  some  practice. 

The  great  scholar  who  held  the  egg  in  his  hand  wdiile 
he  boiled  his  watch,  and  the  other  one  who  dropped  his 
watch  down  the  well  in  place  of  a  stone  when  he  wished 
roughly  to  measure  its  depth,  were  really  thinking  about 
things  vastly  more  important  than  eggs  and  watches. 
There  are  two  kinds  of  absent-mindedness :  the  one 
which  comes  from  extreme  absorption  in  something  else 
(the  philosophical),  and  the  one  which  comes  from 
inability  to  apply  oneself  to  anything  (the  scatter- 
brain). 

The  conditions  of  distraction,  the  effect  of  various 
types  of  training,  the  relative  value  of  different  types  of 
attention,  the  advantages  and  disadvantages  of  distrac- 
tion, such  are  some  of  the  numerous  problems  connected 


ATTENTION  171 

with  this  topic  which  await  solutiou  in  the  experimental 
psychology  of  education. 

7.  Sense  Processes  in  Attention. — Observe  by  intro- 
spection, in  repeated  trials,  and  record  the  sensory  and 
motor  tendencies  which  are  characteristic  of  each  of  the 
following  attitudes  of  attention : 

(a)   The  attitude  of  listening  as  in  Exp.  4. 
(&)   The  effort  to  see  clearly  the  irregularities  in 
the  period  at  the  end  of  this  sentence. 

(c)  Resting  a  finger  upon  the  point  of  a  pin  or 
sharp  penknife  and  observing  the  fluctuation 
in  the  sensation  of  pain  from  the  pricking. 

(d)  Thinking  the  names  of  the  five. largest  towns 
in  your  State,  eyes  closed. 

(e)  Imagining  a  baseball  flying  directly  toward 
your  face. 

All  attitudes  of  attention  have  certain  tendencies  in 
common,  and  each  attitude  probably  has  peculiar  tend- 
encies which  give  characteristic  sensory  impressions.* 

*  Pillsbury  in  his  work  on  "Attention"  sums  up  his  chapter 
on  the  motor  accompaniments  of  attention  as  follows :  ( 1 )  The 
muscles  of  the  sense-organs  contract  so  as  to  give  the  greatest 
efficiency.  (2)  The  voluntary  muscles  of  the  limbs  and  the 
trunk  tend  to  make  contractions  which  have  been  useful  in  sim- 
ilar situations  of  previous  experience.  (3)  There  is  a  tendency 
to  contract  certain  muscles  regardless  of  the  nature  of  the  stimu- 
lus. (4)  The  processes  of  respiration  and  circulation  are  pro- 
foundly affected.  (5)  The  bodily  processes  accompany  attention; 
they  do  not  precede  it. 

It  is  these  motor  processes  that  one  has  sensory  impressions  of 
in  the  state  of  attention. 


CHAPTER  XIV 
NOEMAL  ILLUSI0:N^S 

For  One. 

The  problem  is  to  measure  certain  normal  illusions 
in  visual  perception  of  space.  The  observer  must  bear 
the  following  principles  clearly  in  mind : 

a.  These  illusions  are  normal ;  if  they  do  not  appear 
in  the  record,  that  is  proof  of  either  incompetence  or 
abnormality  in  space  estimation.* 

h.  These  experiments  involve  a  clear  distinction 
between  Avhat  loohs  right  and  what  is  right.  We  shall 
here  devote  attention  to  the  way  things  look,  not  what 
they  really  are.  The  observer  is  asked  to  make  ad- 
justments so  that  they  look  right  according  to  his  very 
best  ability,  but  to  make  any  allowance  on  the  basis  of  a 
guess  or  knowledge  of  the  possible  direction  and  magTii- 
tude  of  the  illusion  is  forbidden.  The  value  of  these 
experiments  depends  upon  the  power  of  self-possession 
in  observing  this  distinction,  and  its  chief  training  value 
also  lies  in  this.  The  assignment  of  this  experiment  is 
an  expression  of  confidence  in  the  ability  and  integrity 
of  the  observer. 

c.  The  observer  must  perform  all  the   experiments 

*  Barring   rare   cases   of   special   training   in   certain   types   of 
illusion. 

J7? 


Plate  I. 


on  ot  space 


r.I:  'I    roro    r-ac^  ^    '■i    -;H'i-ial    1  r:i.ir\iiu!    in    certtt 
.1    3TAJ*^I 


NORMAL  ILLUSIONS  173 

before  checking  any  or  verifying  the  accuracy  of  his 
judgment  hy  any  means  ivliatever."^ 

d.  The  book  should  lie  upon  the  table  in  a  normal 
position  for  reading,  except  when  otherwise  specified, 
and  the  observer  should  maintain  the  same  position  with 
reference  to  it  throughout  the  series  of  experiments. 
This  will  prevent  sighting. 

1.  The  Arc  Terminal  Illusion,  a.  One  Horizontal 
Distance. — Place  three  silver  dollars  or  other  coinSj-j- 
edge  to  edge,  in  a  straight  row  on  the  table.  Remove 
the  middle  coin  and  place  it  to  the  right,  in  the  same 
line,  in  such  a  position  that  the  distance  between  the 
adjacent  edges  of  the  moved  coin  and  the  coin  now  in 
the  middle  shall  be  equal  to  the  original  distance  across 
the  three  coins.  Measure  and  record  the  distance  be- 
tween the  middle  and  right-end  coins,  but  do  not  meas- 
ure the  standard  or  verify  by  it. 

h.  Tivo  Vertical  Distances. — Place  the  three  coins 
edge  to  edge  as  before ;  push  the  middle  one  straight  out 
forward  into  such  a  position  that  the  distance  from  this 
coin  to  each  of  the  other  coins  shall  look  equal  to  the 
original  distance  across  the  three  coins.  Record  the 
two  variable  distances  only. 

In  the  following  experiments  geometrical  figures  are 
made  variable  by  combining  some  figure  in  PL  I  on  the 


*  If,  by  any  adventure  or  slip  in  self-command,  the  observer 
should  gain  objective  knowledge  of  the  validity  of  his  judg- 
ment or  aid  in  the  estimation,  this  must  be  recorded,  as  it  is  sure 
to  influence  the  following  experiments. 

f  In  the  absence  of  coins,  use  three  disks  cut  from  paper. 


174  NORMAL  ILLUSIONS 

tissue-paper  with  some  figure  in  PL  II  or  PL  III.  Tear 
the  tissue-paper  off  at  the  perforation  and  use  it  with 
the  printed  face  down.  As  printed  numbers  or  letters 
in  the  plate  would  be  disturbing  elements,  w^e  may 
simply  agree  upon  the  following  designation  of  the 
figures  in  the  plates : 

PL  II:  A,  the  feathered  figure  at  the  top;  B,  the  second  figure 
from  the  top;  C,  the  slanting  bar  with  the  three  dots;  D,  the 
forked  figure  at  the  bottom. 

PL  III :  A,  the  large  double  figure  in  the  upper  left-hand 
corner;  B,  the  slanting,  crossed  bar  with  its  dot  above;  C,  the 
cylinder  top;  D,  the  parallel  lines;  and  E,  the  horizontal  line. 

2.  The  Angle-line  Terminal  Illusion:  Lengthening 
and  Shortening  Effects. — Place  the  tissue-paper  over 
PL  II  so  that  the  apex  of  the  angle  of  the  figure  on  the 
tissue-paper  lies  over  the  base-line  of  Fig.  A  and  points 
toward  the  left.  Bisect  the  base-line  by  placing  the 
apex  of  the  angle  so  that  it  looks  to  be  at  the  middle  of 
the  line.     Measure  and  record  the  left  section  only. 

3.  The  Angle-line  Terminal  Illusion:  Shifting  Ef- 
fect.— Bisect  the  base-line  of  Pig.  A,  PL  II,  as  above, 
but  use  one  of  the  dots  on  the  tissue-paper  instead  of 
the  apex  of  the  angle  figure  to  mark  the  middle  point. 
Measure  and  record  the  left  section  only. 

4.  The  Secondary- figure  Terminal  Illusion:  Attrac- 
tion of  Regard  in  Length. — Place  the  long  line  of  the 
tissue-paper  to  the  right  of  Fig.  B,  PL  II,  by  the  side  of 
the  book ;  *  cover  one  end  with  a  piece  of  thick  paper 

*  To  measure  in  the  book,  mark  the  distance  with  some  sharp 
point  on  the  edge  of  a  sheet  of  paper  and  then  measure  that  on 
the  millimeter  scale. 


Plate  II. 


NORMAL  ILLUSIONS  177 

and  adjust  this  paper  until  the  exposed  part  of  the 
>.issiie-paper  line  looks  equal  to  the  middle  line  of  Fig. 
B.     Measure  and  record  the  varied  line  only. 

5.  The  Attraction  of  Regard  in  Direction. — Place 
the  tissue-paper  over  Fig.  C,  PI.  II,  so  that  the  short 
line  on  the  tissue-paper  coincides  with  the  line  of  the 
three  dots,  then  slide  the  tissue-paper  upward  and  to- 
ward the  left,  within  the  same  line  marked  by  the  dots, 
until  the  upper  end  of  the  moved  line  looks  to  be  where 
the  lower  line  would  strike  if  continued  upward  in  its 
present  direction  as  a  straight  line.  Measure  and  re- 
cord the  distance  between  the  right  dot  and  the  right 
end  of  the  moved  line  only. 

6.  The  Oppel  Illusion:  The  Bending  Effect,  a. 
Upper  Line. — Place  one  of  the  two  dots  on  the  tissue- 
paper  on  the  joint  of  Fig.  D,  PL  II,  and  turn  the  tissue- 
paper  so  that  the  other  dot  shall  indicate  what  direction 
the  lower  left  line  would  take  if  continued  upward  to 
the  right  as  a  straight  line.  Sighting  is,  of  course,  for- 
bidden. Measure  the  distance  between  the  movable  dot 
and  the  end  of  the  line  above  it  only. 

h.  Lower  Line. — Make  the  same  kind  of  a  measure- 
ment for  the  upper  left  line. 

7.  The  Poggendorff  Illasion:  The  Breaking  Ef- 
fect.— Place  one  of  the  dots  on  the  tissue-paper  over  the 
right  vertical  line  of  Fig.  Ay  PL  III ;  indicate  with  this 
dot  the  point  at  which  the  £hort  slanting  line  at  the  left 
would  strike  if  continued  is  a  straight  line  across  the 


178  NORMAL  ILLUSIONS 

space  between  the  two  verticals.     Measure  and  record 
the  distance  from  the  top  of  the  line  to  the  dot  only. 

8.  The  Zollner  Illusion:  The  Leaning  Effect. — 
Place  one  end  of  the  short  line  on  the  tissue-paper  end 
to  end  with  the  top  of  the  slanting  base-line  of  Fig.  B, 
PI.  Ill,  and  adjust  the  upper  end  of  the  movable  line 
until  it  seems  to  make  a  straight  and  continuous  line 
with  the  base-lin?.  Beware  of  sighting!  Measure  and 
record  the  distance  between  the  upper  end  of  this  line 
and  the  dot  lying  over  toward  the  left. 

9.  The  T-Illusion. — Place  the  long  line  on  the  tissue- 
paper  over  Pig.  E,  PI.  Ill,  so  that  it  crosses  it  at  right 
angles  at  the  middle ;  place  a  sheet  of  thick  white  paper 
over  the  tissue-paper  so  that  its  upper  edge  is  close  to 
and  parallel  with  the  lower  edge  of  the  line  of  Fig.  E ; 
draw  the  tissue-paper  up  or  down  until  the  vertical  line 
thus  formed  above  the  middle  of  the  horizontal  appears 
to  be  equal  to  the  horizontal  in  length.  Measure  and 
record  the  length  of  the  varied  line  only. 

10.  The  Illusion  of  the  Vertical. — Proceed  in  the 
same  manner  and  with  the  same  means  as  in  Exp.  9, 
except  that  you  erect  the  vertical  at  one  end  of  the  line 
in  Fig.  E,  instead  of  at  its  middle. 

11.  The  Illusion  of  Interrupted  Space,  a.  Hori- 
zontal.— Place  the  bar  figure  on  the  tissue-paper  over 
Fig.  D,  PI.  Ill,  so  that  the  bars  coincide  and  adjust  up 
and  down  until  the  whole  figure  looks  square.  Measure 
and  record  the  vertical  dimension  only. 


A 


Plate  III. 


NORMAL  ILLUSIONS  181 

h.  Vertical. — Turn  the  whole  figure  through  90°  and 
make  sidewise  adjustments  until  the  whole  figure  looks 
square.     Measure  the  varied  dimension  only. 

12.  The  Illusion  of  Length  in  the  Cylinder,  -a. 
Vertical. — Lay  the  tissue-paper  over  Fig.  C,  PL  III,  so 
that  the  cylinder  base  on  the  tissue-paper  telescopes  with 
the  cylinder  top  in  the  book ;  adjust  up  and  down  until 
the  length  of  the  cylinder  appears  to  be  equal  to  its 
width.  Measure  the  vertical  distance  between  the  top 
and  bottom  at  the  middle. 

h.  Horizontal.' — Repeat  the  same  measurement  with 
the  cylinder  in  the  horizontal  position. 

If  the  observer  has  shown  fidelity  and  self-control  and 
has  been  honest  enough  in  these  experiments  not  to 
sight  or  check-measure,  he  has  passed  a  good  test  of 
character  and  may  be  recommended  for  a  position  of 
trust.  The  records  also  constitute  a  measure  of  the 
power  of  discrimination  in  visual  perception  of  space. 

The  first  lesson  one  learns  in  the  study  of  sense-per- 
ception is  that  ''the  senses  deceive".  The  second  lesson 
is  that  ''there  is  system  in  the  deception"  ;  being  warned 
of  the  presence  of  danger,  we  may  become  the  masters 
of  our  senses  and  avert  the  deception.  Both  these  les- 
sons are  contained  in  the  above  experiments,  which  are 
intended  to  show  that  there  are  certain  universal 
motives  for  illusion  and  that  it  is  possible  to  determine 
their  approximate  force  and  thus  become  able  to  make 
due  allowance  for  them. 

Now,  let  the  obser\^r  turn  back  to  the  figures  and 
records  and  reproduce  the  setting  for  each  figure   (1) 


182^  NOEMAL  ILLUSIONS 

according  to  the  record,  (2)  according  to  the  standard 
measurement  given  below,  and  (3)  according  to  the 
average  record  given  below.  In  stating  the  magnitude 
of  the  normal  illusions,  it  will  be  given  with  reference 
to  a  normal  adult  male  wlio  is  a  reliable  observer  and 
is  not  acquainted  with  the  illusion.  The  illusion  varies 
with  age,  sex,  knowledge  of  the  illusion,  power  of  con- 
centration, etc.  Thus,  one  of  the  laws  of  illusion  is 
that  knowledge  of  the  nature  and  force  of  the  illusion 
decreases  it,  often  by  as  much  as  one  half  its  force; 
hence  the  illusion  measurement  in  the  first  record 
should  now  seem  too  large. 

The  standard  distance  in  Exp.  1  is  114  millimeters 
for  dollars  or  disks.  The  average  normal  observer 
makes  the  distance  about  100  millimeters  in  1  a,  which 
means  an  illusion  of  12  per  cent.  The  error  is  much 
greater  in  1  & ;  normally  it  amounts  to  more  than  20  per 
cent. 

This  form  of  the  terminal  illusion  is  very  common  in 
ordinary  perception.  The  simplest  form*  of  it  is  where 
we  compare  the  distance  between  two  more  or  less  round 
bodies  with  the  diameter  of  one,  as  in  Fig.  30.*  Of 
course  the  illusion  does  not  rest  upon  the  comparison. 
The  diameter  of  the  figure  is  underestimated  and  the 
distance  between  the  two  figures  is  overestimated,  inde- 
pendently of  the  comparison,  as  may  be  determined  by 
measuring  each  in  terms  of  a  plain  line.     We  need  only 

*  Fig.  30.  This  is  a  copy  of  a  small  section  of  wall-paper. 
The  aim  of  the  artist  has  been  to  produce  the  effect  of  the  ratio 
1:1,  which  is  the  impression  obtained  by  the  average  observer, 
but  the  distance  between  the  figures  is  actually  10  per  cent 
smaller  than  the  distance  across  one  figure. 


NOKMAL  ILLUSIONS 


183 


look  intelligently  at  our  wall-papers,  carpets,  bed-covers, 
table-linen,  and  patterns  in  dress  goods  to  find  evidence 
of  this  illusion.  The  commonest  effects  sought  by 
artists  are  approximately  the  ratios  1:1  and  1 :1.6. 
Find  designs  which  give  these  effects  to  the  eye  when  the 
terminals  of  the  distance  are  arc-formed,  and  measure 
them,  and  you  will  find  that  the  artist  has  made  allow- 
ance for  the  illusion,  usually  8  to  12  per  cent.  The 
designer  of  patterns  makes  free-hand  sketches  by  eye 


Fig.  30, 


estimate  and  thus  naturally  makes  the  proper  allowance 
for  the  illusion.  Where  distances  of  this  kind  are  made 
equal  they  do  not  look  equal. 

In  Exp.  2  the  true  distance  is  34  millimeters.  The 
force  of  the  illusion  is  approximately  the  same  as  in 
Exp.  la;  that  is,  the  measured  section  is  made  about 
12  per  cent  too  short.  This  is  a  double  figure,  because 
one  section  has  the  lengthening  effect  and  the  other  has 
the  shortening  effect.     It  combines  two  complementary 


184  NOKMAL  ILLUSIONS 

illusions.  Each  of  these  might  be  measured  separately 
in  terms  of  a  plain  line.  The  left  end  has  the  lengthen- 
ing effect  and  the  right  end  has  the  shortening  effect. 
The  figure  is  also  called  ''full-fledged"  because  it  has  a 
full  set  of  end  lines ;  a  single  line  would  produce  the 
illusion,  though  not  so  forcibly. 

This  illusion  is  very  common  in  objects  around  us,  as 
in  trees,  fences,  and  lawn-patches,  as  well  as  in  designs 
and  structural  effects,  in  fact  in  all  sorts  of  objects  in 
which  a  linear  distance  is  marked  off  at  one  or  both  ends 
by  one  or  more  end  lines. 

In  Exp.  3  the  true  distance  is  again  34  millimeters, 
but  the  measured  section  is  usually  made  from  3  to  6 
per  cent  too  short.  This  means  that  the  center  of  the 
base-line  is  shifted  to  the  left  by  that  amount. 

When  we  bear  in  mind  that  it  is  not  necessary  that' 
all  the  end  lines  should  be  present,  we  can  realize  how 
commonly  the  conditions  for  the  shifting  effect  are 
present  in  nature  and  art.  The  twigs  on  a  limb  seem 
farther  up  than  they  are.  The  middle  point  between 
two  branches,  one  above  the  other,  is  not  where  it  seems 
to  be.  The  cross-line  on  the  letter  A  seems  lower  than 
it  really  is. 

In  Exp.  4  the  true  length  is  52  millimeters,  but  the 
varied  line  is  probably  made  from  4  to  8  per  cent  too 
long.  This  again  is  a  very  common  situation  in  all 
that  we  see.  Teclmicallj^  we  say  the  perception  of  a 
primary  stimulus  is  influenced  by  secondary  stimuli. 
The  visual  length  of  an  object,  Avhatever  it  may  be, 
varies  with  the  presence  of  other  objects  near  its  ends. 

The  first  four  experiments  deal  with  the  terminal 


NORMAL  ILLUSIONS  186 

illusion  of  which  the  angle-line  figure^  generally  known 
as  the  Miiller-Lyer  figure,  is  the  most  familiar  type. 
They  all  illustrate  the  principle  that  the  appearance  of 
a  linear  distance  is  modified  by  the  presence  of  terminal 
forms.  These  forms  may  be  grouped  roughly  into  three 
classes ;  namely,  the  arc,  the  angle-line,  and  the  detached 
or  secondary  figures.  The  last  named  are  not  terminals 
in  the  strict  sense,  as  the  line  is  clear-cut  in  itself,  but 
psychologically  they  operate  as  terminals,  for  we  cannot 
look  at  the  middle  line  without  having  our  ' 'regard"  at- 
tracted to  the  end  lines. 

The  terminal  illusion  effects  may  also  be  grouped  into 
three  classes:  the  lengthening,  the  shortening,  and  the 
shifting.  The  lengthening  effect  is  illustrated  in  Exps. 
1,  2,  and  4,  and  is  the  result  of  outward-pointing  arcs, 
angle-lines,  or  secondary  features.  The  shortening 
effect  is  illustrated  in  Exps.  1  and  2  (the  right  half) 
and  is  the  result  of  the  inward-pointing  terminal.  The 
shifting  effect  is  illustrated  in  Exp.  3  and  is  due  to  the 
fact  that  the  angle-lines  point  in  the  same  direction. 

The  strength  of  the  terminal  illusion  varies  with  a 
vast  number  of  conditions  in  the  object,  such  as  the 
length  of  the  terminals,  the  angle  of  the  terminals,  the 
number  of  terminals,  the  body  of  the  terminals,  the 
relative  size  of  the  figures,  the  vagueness  of  the  ter- 
minals, adjacent  objects,  complexity  of  the  figure,  mean- 
ing of  the  figure  or  object,  time  of  exposure,  etc.  As  a 
rule  the  illusion  is  decidedly  stronger  in  natural  ob- 
jects than  in  geometrical  figures.  It  varies  also  with 
subjective  conditions,  such  as  power  of  visualizing, 
training,  concentration  of  attention,  mode  of  regarding, 


186  NOEMAL  ILLUSIONS 

knowledge  or  suspicion  of  its  existence,  etc."^  Each  and 
all  such  variables  may  be  made  the  object  of  experi- 
ment. Indeed  certain  laws  have  been  w^orked  out  by 
measurements  upon  every  factor  here  named. 

The  same  illusion  obtains  for  the  sense  of  touch. 

The  first  four  experiments  illustrate  a  certain  type 
of  illusion  of  length ;  the  next  four  illustrate  illusions  of 
direction.  The  two  groups  find  a  natural  transition  in 
that  Exp.  4,  the  last  in  the  former  gTOup,  and  Exp.  5, 
the  first  in  the  present  gTOup,  are  both  conspicuous  il- 
lustrations of  so-called  ''attraction  of  regard".  This 
term  is  used  in  both  the  physical  and  the  mental  sense : 
the  physical  eye  and  the  "mind's  eye"  are  both  at- 
tracted. That  is  a  principle  w^hich  runs  through  both 
groups. 

In  Exp.  5  the  true  measurement  is  11  millimeters. 
The  observer  probably  made  it  about  10  millimeters; 
that  is,  the  adjustable  line  was  not  pushed  far  enough 
forw^ard.  This  deflection  of  the  apparent  projection 
of  the  lower  line  w^as  caused  by  the  attraction  of  the 
upper  line.  How  often  do  we  judge  direction  of  a  line 
without  the  presence  at  one  side  of  some  other  line  or 
object  ? 

In  Exp.  6  a  the  dot  is  placed  too  high  by  about  2 
millimeters ;  the  true  measure  is  13  millimeters.  In 
Exp.  6  h  the  dot  is  placed  too  low  by  about  3  milli- 
meters; the  true  measure  is  26  millimeters.  If  the 
low^er  left  line  were  actually  drawn  straight  in  extension 
by  a  ruler,  a  close  observer  would  see  an  apparent  bend 


*  These  illustrations  are  typical  of  variables  in  the  other  eight 
iypes  of  illusion  also. 


NORMAL-  ILLUSIONS 


187 


at  the  joint.  Figures  31  and  32  are  rather  striking 
illustrations  of  the  Oppel  type  of  small-angle  illusion.* 

In  Exp.  7  the  dot  is  placed  from  6  to  10  millimeters 
too  low,  often  more  than  this.  The  true  measure  is  21 
millimeters. 

In  Exp.  8  the  measurement  usually  shows  a  deflection 
of  2  millimeters  from  the  straight  line.  The  Zollner 
effect  is  illustrated  in  Eig.  33. 

The  figiires  in  Exps.  6,  7,  and  8  may  be  considered 
examples  of  the   ''small-angle   illusion" ;   not   that   the 


Fig.  31. 


small  angle  is  an  essential  condition  for  the  illusion,  nor 
that  it  is  an  explanation,  but  because  it  is  the  principal 


*  Fig.  31.  The  two  horizontal  lines  are  straight  and  parallel,  but 
they  look  bent  on  account  of  the  cumulative  effect  of  the  Oppel 
illusion. 

Fig.  32.  The  circle  and  the  inscribed  square  are  perfect;  but 
if  the  square  is  seen  square,  the  circle  looks  indented.  If  the 
circle  is  seen  as  a  circle,  the  sides  of  the  square  look  curved 
inward. 

Fig.  33.  The  Zollner  pattern.  The  columns  seem  to  topple  or 
lean  by  pairs,  although  they  are  parallel.  The  Poggendorff  effect 
makes  the  short  transversals  seem  discontinuous  or  broken. 
There  is  also  a  false  perspective;  the  columns  seem  to  form 
9,lternate  ridges  or  troughs. 


188 


NOKMAL  ILLUSIONS 


feature  which  they  have  in  common.     The  small  angle 
is  overestimated  in  all  these  cases.     The  effects  of  the 


Fig.  32. 


three   cases  may  be   called,   respectively,   the   bending 
effect,  the  breaking  effect,  and  the  leaning  effect. 


These  figures  represent  situations  that  are  not  un- 
common in  nature,  industry,  and  art.     When  a  straight 


NOKMAL  ILLUSIONS  189 

line  crosses  concentric  circles,  the  Oppel  effect  is  at  its 
best.  Whenever  a  line  strikes  another  at  a  small  angle, 
this  angle  looks  larger  than  it  really  is  and  this  results 
in  an  apparent  bend,  deflection,  or  break  of  the  line. 
AVherever  a  line  or  a  long  object  is  crossed  by  other 
lines  or  objects  at  a  small  angle,  it  suffers  a  deflection. 

The  builders  of  the  Parthenon  were  well  aware  of 
what  is  now  called  the  Oppel  effect,  and  made  correc- 
tions for  it  by  making  lines  that  should  look  straight 
curve  just  enough  to  correct  for  the  illusion. 

In  Exp.  9  we  have  an  illusion  which  is  exceedingly 
variable  and  seems  to  depend  particularly  upon  the 
discriminating  effort  one  puts  forth.  The  variable  is 
frequently  made  from  20  to  30  per  cent  too  short.  The 
standard  is  34.5  millimeters.  The  illusion  can  reach 
this  alarming  force  because  it  is  the  result  of  the  co- 
operation of  several  motives  for  illusion.  Where  can 
one  turn  without  seeing  examples  of  it  ?  Observe  a 
capital  T  and  then  measure  the  proportions.  The  com- 
parison of  the  height  and  the  arm-reach  of  a  man  stand- 
ing with  arms  outstretched  is  a  good  illustration. 

In  Exp.  10  we  have  the  well-known  illusion  of  the 
vertical.  A  good  observer,  who  is  aware  of  the  illusion, 
will  make  the  variable  line  from  5  to  8  per  cent  too 
short.     The  standard  is  34.5  millimeters. 

In  Exp.  11  there  is  an  illustration  of  the  overestima- 
tion  of  filled  as  compared  with  empty  space.  The  vari- 
able dimension  is  made  about  right  in  the  vertical  posi- 
tion and  from  10  to  15  per  cent  too  short  in  the  hori- 
zontal. This  result  is  due,  in  the  latter  case,  to  the  co- 
operation of  this  illusion  with  the  illusion  of  the  ver- 


190  NOKMAL  ILLUSIONS 

tical,  and  in  the  former  case,  to  the  opposition  of  these 
two  approximately  equal  motives  for  illusion. 

In  Exp.  12  a  the  vertical  length  is  probably  made 
more  than  20  per  cent  too  short.  This  is  due  to  the  co- 
operation of  at  least  four  motives  for  illusion.  When 
the  measurement  is  made  in  the  horizontal  position, 
Exp.  12  by  three  of  these  motives  are  counteracted  by 
the  illusion  of  the  vertical  and  the  illusion  is  probably 
reduced  nearly  one  half. 

The  length  of  a  barrel,  the  depth  of  a  teacup,  and  the 
height  of  a  tank  are  overestimated  on  these  principles. 
If  a  person  is  asked  to  estimate  the  height  of  a  silk  hat 
in  comparison  with  the  diameter  of  the  crown,  he  will 
overestimate  the  height  by  more  than  20  per  cent. 

Each  experiment  represents  a  very  large  field  for  il- 
lusion. There  are  normal  illusions  in  all  the  senses  and 
within  each  attribute  of  each  sense.  Thus,  in  sight,  we 
have  illusions  of  color,  space,  movement,  duration,  and 
intensity,  and  each  of  these  covers  numerous  types. 


CHAPTER  XV 
AFFECTIVE^TONE 

For  Two. 

1.  Color  Preferences — Each  of  the  eighteen  colors 
supplied  in  the  book  envelope  is  to  be  compared  with 
every  other  for  the  purpose  of  securing  systematic  ex- 
pressions of  preference.* 

In  each  note-book  cross-rule  a  page  into  nineteen 
spaces  in  the  horizontal  direction  and  nineteen  in  the 
vertical.  Insert  vertical  and  horizontal  headings  as 
in  the  table  beloAV,  which  gives  numerical  order  to  the 
six  colors  and  their  respective  tints  and  shades. 

Lay  a  white  paper  in  such  a  position  on  a  board  or 
book  that  it  shall  be  at  right  angles  to  O's  line  of  vision, 
in  good  light  and  comfortable  position  for  him.  Present 
two  colors  at  a  time,  placing  them  systematically  about 
an  inch  apart  on  the  white  paper,  and  require  O  to 
decide  which  of  the  two  is  more  pleasing  or  less  dis- 
pleasing. The  decision  should  be  immediate  and 
intuitive,  and  free  from  associations. f     The  table  shows 

*  This  experiment  is  based  on  Titehener,  "Experimental  Psy- 
chology,  Qualitative,"   Ch.   XXI. 

f  Avoid  theorizing  or  catering  to  what  ought  to  be  or  what 
would  give  the  best  showing  as  an  expression  of  culture,  etc. 
Let  it  be  a  naive  and  sincere  expression  of  preference  entirely 
independent  of  the  use  of  the  colors. 

191 


192 


AFFECTIVE  TONE 


the  order  in  which  the  comparisons  should  be  made ;  thus, 
1  and  2,  1  and  3,  2  and  3,  2  and  4,  3  and  4,  3  and  5,  etc. 
Let  O  call  the  order  of  colors  to  be  presented,  following 
the  order  shown  in  the  table,  and  keep  the  record  of  his 
preferences  in  the  prepared  blank,  simply  inserting  the 


1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

Rt 

R 

Rs 

OS 

O 

oti 

l^t 

Y 

Ys 

Gs 

G 

Gt 

Bt 

B 

Bs 

Vs 

V 

2 

R 

1 

3 

Rs 

2 

3 

4 

OS 

34 

4 

5 

5 

O 

35 

36 

6 

7 

6 

Ot 

63 

37 

38 

8 

9 

7 

\t 

64 

65 

39 

40 

10 

11 

8 

1: 

88 

66 

67 

41 

42 

12 

13 

9 

iLS 

89 

90 

68 

69 

43 

44 

14 

15 

10 

Gs 

109 

91 

92 

70 

71 

45 

46 

16 

17 

11 

G 

110 

111 

93 

94 

72 

73 

47 

48 

18 

19 

12 

Gt 

126 

112 

113 

95 

96 

74 

75 

49 

50 

20 

21 

13 

Bt 

127 

128 

114 

115 

97 

98 

76 

77 

51 

52 

22 

23 

14 

B 

139 

129 

130 

116 

117 

99 

100 

7b 

79 

53 

54 

24 

25 

15 

Us 

140 

141 

131 

132 

118 

119 

101 

102 

80 

81 

55 

56 

26 

27 

16 

Vs 

148 

142 

143 

133 

134 

120 

121 

103 

104 

82 

83 

57 

58 

28 

29 

17 

V 

149 

150 

144 

145 

135 

136 

122 

123 

105 

106 

84 

85 

59 

60 

30 

31 

18 

vt 

153 

151 

152 

146 

147 

137 

lae 

124 

125 

107 

108 

86 

87 

61 

62 

32 

33 

number  of  the  color  which  he  prefers  in  the  square 
which  forms  the  intersection  of  the  spaces  that  run  to 
the  two  numbers  he  called.  Foot  up  the  results  in  the 
table  so  as  to  show  the  total  number  of  times  that  each 
color  was  preferred. 


AFFECTIVE  TONE  193 

To  express  the  results  graphically,  take  a  sheet  of 
cross-section  paper,  or  cross-rule  one  like  the  above  table 
blank ;  transfer  the  headings  of  the  table  to  the  base-line 
and  number  the  horizontal  lines  from  one  to  eighteen, 
counting  the  base-line  zero ;  make  a  dot  in  each  vertical 
column  on  the  horizontal  line  which  denotes  the  number 
of  times  the  respective  colors  were  preferred,  and  con- 
nect these  dots  with  one  bold  line,  which  will  then  be 
the  curve  of  color  preference. 

It  is  customary  to  speak  of  agreeableness  or  disagree- 
ableness  of  experiences  as  their  affective  tone.  Our 
affective  responsiveness  is  a  matter  of  taste.  It  is  well 
known  that  we  have  our  likes  and  dislikes  for  colors, 
and  that  our  tastes  may  differ  radically. 

Here  we  have  worked  out  a  detailed  expression  of  the 
observer's  taste  for  color  under  the  present  conditions. 
It  would  vary  for  the  same  observer  under  other  condi- 
tions, and  some  of  the  doubtful  cases  might  be  changed 
in  another  trial,  but'  that  throws  no  discredit  upon  the 
experiment  which  depicts  the  observer's  type. 

Individual  differences  are  marked.  One  type  pre- 
fers the  pure  colors,  another  the  tints,  another  the 
shades ;  one  type  prefers  the  soft,  artistic  tints  and 
shades  as  opposed  to  the  bright  hues;  another  type  has 
one  or  more  favorite  hues,  tints,  or  shades,  etc.  The 
curves  give  good  profiles  of  each  type. 

Such  measures  can,  of  course,  be  used  effectively  for 
individual  psychology.  Science,  literature,  and  art 
are  interested  in  race  comparisons  and  in  knowing  the 
culture  history  of  color  preferences  from  the  anthro- 
pological point  of  view.     The  teacher  is  interested  in 


194  AFFECTIVE  TONE 

knowing  the  color  sclienie  of  the  child's  temperament. 
Most  of  us  pass  through  important  changes  in  color 
preferences  as  we  pass  from  childhood  into  mature  age. 
And,  as  a  mode  of  teaching  the  significance  of  color 
values,  the  method  could  be  used  effectively. 

On  the  other  hand,  the  psychologist  takes  only  a 
secondary  interest  in  such  directly  practical  uses.  The 
chief  value  of  experimental  methods  of  studying  affec- 
tive life  lies  in  the  insight  they  favor  and  the  aid  they 
give  in  the  study  of  the  unfoldment  and  explanation  of 
the  laws  of  its  behavior.  This  particular  exj^eriment 
reveals  nothing  in  regard  to  the  reasons  for  color  pref- 
erences, unless  it  be  that  the  introspection  may  give 
some  suggestion.  But  it  is  by  patient  and  ingenious 
employment  of  methods  like  this  under  controlled  and 
variable  conditions  that  we  shall  evolve  the  real  ex- 
planation of  color  preferences. 

We  know  now,  in  general,  that  the  affective  value  of 
color  depends  upon  the  specific  physiological  action 
of  each  color,  the  purpose  the  color  serves,  and  habits  of 
association.  Our  experiment,  which  shows  the  actual 
preferences,  then  naturallj^  suggests  three  corresponding 
lines  of  research  in  answer  to  the  question,  Why  is  one 
color  preferred  to  another  ? 

There  is  a  tendency  in  ?esthetics  at  the  present  time 
to  look  for  physiological  explanation  of  modes  of  agTce- 
ableness  and  disagreeableness.  What  are  the  character- 
istic physiological  actions  of  each  color?  In  attempt- 
ing to  answer  that  question,  the  experimenter  profitably 
starts  from  analogies  of  known  effects  upon  low^er  forms 
of  animal  life  and  plant  life.     Fruits  and  flowers  grown 


AFFECTIVE  TONE  195 

in  experimental  greenhouses  each  covered  by  a  different 
color  of  glass  show  great  differences  in  growth  and  de- 
velopment. The  red  light  acts  like  a  fertilizer  on  the 
soil,  while  blue  and  violet  light  check  growth  and 
produce  a  sort  of  dormant  condition  in  the  plants. 
Finsen's  discovery  of  the  curative  value  of  the  ultra- 
violet rays  rests  upon  the  principle  that  these  rays  kill 
certain  disease-germs  in  the  human  tissue.  The  same 
rays,  however,  favor  the  development  of  various  larvae, 
tadpoles,  etc.  Color  rays  strike  the  most  sensitive  form 
of  living  tissue,  the  nervous  system,  through  the  eye. 
Ordinarily  we  become  conscious  of  these  affective  dif- 
ferences in  effect  only  in  attitudes,  general  aware- 
ness of  ill-being  or  well-being.  One  color  is  excit- 
ing, another  is  soothing,  one  is  fatiguing,  another  is 
restful,  etc.  Shall  the  explanation  of  such  a  physi- 
ological action  be  given  in  large  part  in  terms  of 
chemistry  ? 

The  second  question  would  search  into  the  signif- 
icance of  the  uses  of  colors.  Take  red,  for  example. 
Red  is  the  symbol  of  joyous  emotion.  It  is  the  symbol 
of  sacred  rights,  of  royal  power,  of  victory,  of  pledged 
sincerity,  and  of  love.  It  is  the  first  color  to  interest 
primitive  man.  Words  for  red  are  the  first  color  terms 
to  develop  in  nearly  all  primitive  communities ;  a  tribe 
may  have  half  a  dozen  synonyms  for  red  before  it  has 
any  name  for  blue  or  green.  Children  seem  to  repeat 
the  tendencies  of  the  race.  Red  is  the  primitive  color 
for  decoration;  men  and  women  smear  themselves  with 
red  ochre  and  paint  their  utensils  and  implements  in 
brilliant  reds.     Red  is  the  dominating  tone  of  color  in 


196  AFFECTIVE  TONE 

religious  rites,  at  the  wedding,  and  at  the  conclave.  It 
is  conspicuously  absent  in  mourning.  Children,  if  un- 
influenced, tend  to  use  red  more  than  any  other  color. 
In  abnormal  sensitiveness  it  is  red  that  jars  most. 
The  hysteric  is  conscious,  at  times,  of  nothing  but  red. 
Likes  and  dislikes  for  it  are  strong.  The  red  flag  is  the 
rallying-point  for  the  anarchist.  It  is  the  symbol  of 
excitement  in  epidemics.  In  brief,  red  is  the  color  of 
ripe  fruit,  it  is  the  color  of  the  flame,  and  of  blood. 

Aside  from  the  physiological  conditions  and  the  uses 
of  colors  there  is  a  third  type  of  problems  which  pertain 
more  specifically  to  the  explanation  of  the  habits  of 
association.  To  what  extent  can  color  preferences  be 
cultivated  ?  What  is  the  biological  explanation  for  the 
survival  of  certain  types  of  color  preferences  ?  What  is 
the  reason  for  the  order  of  development  of  color 
preference  in  the  race  ?  In  the  child  ?  The  present 
tendency  is  toward  the  so-called  artistic  colors ;  is  that  a 
permanent  characteristic  of  developed  mental  life  ? 

Let  us  notice  some  instances  of  the  use  of  the  method 
of  this  experiment  in  the  study  of  other  affective  values. 

The  matching  of  color  is  an  important  item  in  dress, 
in  the  finishing  and  furnishing  of  a  room,  in  art,  and  in 
many  industries.  The  psychologist  must  lay  a  founda- 
tion for  canons  of  color  harmony  by  working  out  the 
fundamental  laws  of  affective  value  of  color  combina- 
tions independently  of  their  use.  It  has  never  been 
done  thoroughly.  The  thing  to  do  is  to  select  a  suitable 
series  of  colors  and  grays  and  treat  a  match  of  any  two 
of  these  as  the  unit  of  the  experiment ;  thus,  the  agree- 
ableness  of  a  red  matched  with  a  green  may  be  compared 


AFFECTIVE  TONE  197 

with  a  match  of  red  with  a  dark  orange  shade. 
Each  color  (or  gray)  must  be  matched  with  every  other 
color,  and  each  match  must  be  compared  with  every 
other  match.  From  a  well-established  curve  of  such 
results  the  laws  of  color  harmony  might  be  stated.  But 
when  these  laws  are  to  be  applied  in  art  and  industries, 
the  individual  variation,  accessory  influences,  etc.,  must 
be  taken  into  account,  and  the  problem  grows  more 
complicated. 

The   curve   Fig.    34    (from   Wundt)    expresses   the 
results  of  some  experiments  by  a  cruder  method,  show- 


Dark-btue 


Bright-red 


Red 

Orange 


Ir'/U/tt 

Fig  34 


ing  the  affective  curves  of  matches  with  red.  Height 
above  the  base-line  represents  degree  of  agreeableness  of 
the  match  of  red  with  a  given  color,  whereas  depth 
below  shows  degree  of  disagreeableness  of  a  combina- 
tion. Thus,  red  makes  pleasing  combinations  with 
other  colors  in  the  order  dark  blue,  green,  bright  red, 
dark  red,  and  displeasing  combinations  with  violet  and 
orange.  The  greatest  agreeableness  is  approximately  at 
the  greatest  opposition  (complementary  color),  and 
there  is  a  general  depression  into  disagreeableness  on 
each  side  of  this  crest. 


198 


AFFECTIVE  TONE 


In  selecting  our  stationery,  in  designing  a  table-top, 
in  platting  our  flower-garden — in  short,  wherever  a 
rectangular  surface  is  designed  to  be  pleasing  in  propor- 
tions, we  may  look  to  empirical  psychological  laws  for 
guidance.  The  relative  agreeableness  or  disagreeable- 
ness  of  different  proportions  of  a  parallelogram  is  ex- 
pressed in  Fig.  35  (from  Wundt,  based  on  Witmer).  A 
series  of  white  cards  of  equal  height  but  varying  length 
have  been  compared  by  a  method  allied  to  the  one  we 
have  used.     The  length  of  cards  in  proportion  to  their 


Fig.  35. 

height  is  laid  off  on  the  base-line.  Elevation  above  that 
line  indicates  relative  agreeableness  of  such  proportions, 
and  depression  means  corresponding  disagreeableness. 
Thus,  the  most  pleasing  ratio  centers  around  1 :1.6, 
which  is  known  as  the  golden  section  or  golden  cut.* 


*  The  golden  section  for  the  rectangle  is  that  in  which  the 
short  side  is  to  the  long  side  as  the  long  side  is  to  the  sum  of 
the  long  and  the  short  sides.  This  proportion  may  be  applied  to 
various  forms  such  as  crosses  and  complex  designs.  A  study  of 
jewelrj^  stationery,  monuments,  etc..  reveals  a  most  remarkable 
adherence  to  these  proportions.  The  commonest  cross  is  in  that 
proportion;  the  upper  section  of  the  upright  is  to  the  lower  sec- 
tion as  the  lower  section  is  to  the  whole  upright.  It  has  been 
pointed  out  that  many  of  the  forms  of  nature  are  shaped  in  this 
proportion.  Tables,  lapboards,  and  mountings  for  apparatus 
made  according  to  the  golden  section,  in  the  writer's  laboratory, 
give  a  pleasing  effect. 


AFFECTIVE  TONE  199 

The  square  is  decidedly  disagreeable,  but  the  apparent 
square  *  is  agreeable,  although  not  so  agreeable  as  the 
golden  section.  A  parallelogram  that  is  a  little  longer 
than  the  apparent  square  is  disagreeable. 

The  method  may  be  used  with  equally  good  effect  in 
hearing.  Music  depends  upon  the  agreeableness  of 
certain  tone-intervals.  Different  nations  have  different 
scales,  and  there  is  a  process  of  gradual  evolution  of 
musical  scales.  Some  of  the  intervals  are  ''natural", 
other  intervals  are  more  or  less  arbitrary.  There  is  an 
instrument  called  a  tone-variator  with  which  we  can 
produce  any  desired  interval.  Suppose  that  we  divide 
one  octave  into  one  hundred  equal  steps  and  ahvays  use 
the  fundamental  as  one  of  the  two  tones.  By  compar- 
ing each  of  "the  hundred  intervals  in  such  a  series  wdth 
every  interval  in  the  series,  we  may  establish  a  curve  of 
the  relative  agTceableness  of  these  intervals.  Such  a 
curve  will  contain  a  large  number  of  waves  of  different 
amplitude,  the  crests  indicating  consonant  tones  and  the 
troughs  dissonant.  What  light  would  such  a  curve 
throw  upon  our  conventional  musical  scale  ?  It  would, 
of  course,  reveal  the  natural  intervals  and  show  the 
order  of  their  preference,  and  then  it  would  show  other 
desirable  intervals  in  the  order  that  they  are  agreeable. 
It  w^ould  show  how  arbitrary  certain  parts  of  our  scale 
are. 

These  stimuli  are  not  of  any  rousing  emotional  tone. 
If  we  should  take  smell  and  taste  stimuli,  we  should 
realize  more  fully  the  fact  that  we  are  dealing  with 
emotional  factors. 

*  Due  to  the  illusion  of  the  vertical. 


200  AFFECTIVE  TONE 

At  this  point  we  must  impress  the  warning  that  there 
is  danger  of  making  these  measurements  seem  too 
simple  and  too  immediately  serviceable.  Emotional 
life  is  more  individualized  than  cognitive  life.  We  can- 
not set  up  the  curve  of  one  individual  as  the  norm  for 
aV  others,  nor  can  we  take  the  average  of  a  large  number 
of  curves  and  exj^ect  one  individual  to  fit  that.  The 
conclusions  must  also  be  rigorously  limited  to  the  condi- 
tions under  which  they  are  taken.  Thus,  the  agreeable- 
ness  of  a  tone-interval  depends  upon  its  sequence,  the 
harmony  of  the  colors  depends  upon  the  background,  the 
agreeableness  of  taste  depends  upon  its  relation  to  other 
tastes,  etc. 

But  these  are  matters  which  may  in  turn  be  made 
the  object  of  study.  It  is  possible  to  determine  sta- 
tistically the  degree  of  variability  among  individuals 
in  affective  responses.  Instead  of  covering  them 
over,  measurement  reveals  individual  differences.  Be- 
fore a  curve  is  used  we  must  know  its  coefficient  of 
variability. 

There  are  two  general  types  of  method  that  may  be 
employed  in  studying  feeling :  the  method  of  impression 
and  the  method  of  expression.  The  above  is  a  method 
of  impression.  That  is,  the  experiment  simply  favors 
accurate  formation  and  recording  of  impressions.  Im- 
pression methods  may,  of  course,  be  used  in  a  great 
variety  of  ways.  In  the  expression  methods  some  ob- 
jective bodily  expression  of  feeling  is  measured. 
Among  these  are'  effects  upon  the  bodily  strength,  in- 
voluntary movements,  volume  of  certain  parts  of  the 
body,   circulation,   breathing,   secretions,  etc.     Exp.   2 


AFFECTIVE  TONE  201 

will  illustrate,  in  a  crude  way,  the  characteristic  expres- 
sions in  involuntary  movements. 

2.  Affective  Expressions  in  Involuntary  Move- 
ments.— The  object  of  the  experiment  is  to  determine 
what  direction  the  involuntary  movements  of  the 
balanced  hand  shall  take  in  smelling  an  agreeable  or  a 
disagreeable  odor. 

Invite  some  one  who  knows  nothing  about  this  kind 
of  experiments  to  act  as  observer,  as  the  response  is 
influenced  by  a  knowledge  of  the  condition  of  the  ex- 
periment."^ 

Select  some  substances  that  have  decidedly  agreeable 
or  disagreeable  odor  such  as  perfumes,  flowers,  ammonia, 
and  vinegar. t     Keep  these  in  an  adjoining  room. 

Blindfold  the  observer  and  ask  him  to  stand  erect  and 
firm  and  hold  his  hand  about  a  foot  in  front  of  his  face. 
Direct  him  to  say  whether  an  odor  is  agreeable  or  dis- 
agreeable to  him  when  he  smells  it. 

'Now  let  one  of  the  experimenters  hold  one  of  the 
odoriferous  substances  under  the  observer's  nostrils 
three  seconds,  so  that  he  gets  a  good  whiff  of  the  odor. 
Let  the  other  experimenter  take  an  advantageous  posi- 
tion for  observation  of  the  movements  of  the  hand  and 

*  When  everything  is  ready,  it  should  not  take  more  than 
five  minutes  to  perform  the  experiment.  Proceed  with  the  alert- 
ness of  a  photographer  and  take  the  invited  observer  unawares. 
Tell  him  that  you  wish  to  test  his  feelings  of  agreeableness  and 
disagreeableness  for  odors,  and  give  no  intimation  by  word  or 
sign  about  your  interest  in  his  movements.  You  must  keep  his 
attention  away  from  his  hand. 

t  One  of  each  kind  will  do  if  decided,  but  it  is  very  advan- 
tageous to  have  a  good  assortment.  Care  must  be  taken  that 
the  agreeable  odor  is  not  too  strong. 


202  AFFECTIVE  TONE 

trace  on  paper  the  approximate  direction  and  magnitude 
of  the  movement  which  is  made  the  moment  the  ob- 
server perceives  the  odor.  Kecord  with  this  the  odor 
nsed  and  the  observer's  statement  abont  it.  Make 
about  five  trials  with  agreeable  and  -Q-ve  with  disagree- 
able odors. 

Agreeable  odors  have  a  tendency  to  cause  the  hand 
to  reach  out  away  from  the  body,  while  disagreeable 
odors  have  a  tendency  to  cause  a  flexion  of  the  arm  mov- 
ing the  hand  toward  the  body. 

These  movements  are  unconscious  rudimentary  re- 
actions which  do  not  serve  any  purpose.  They  are  re- 
flexes which  repeat  in  miniature  the  general  tendencies 
of  action  which  have  as  a  rule  been  beneficial.  The 
principle  might  be  stated  more  freely  as  follows :  When 
the  stimulus  is  felt  as  agreeable  the  hand  makes  the 
inceptive  movement  to  get  more  of  it;  while,  if  the 
stimulus  is  felt  as  disagreeable,  the  hand  makes  the  in- 
ceptive fending  movement  for  the  purpose  of  getting 
it  away.  This  tendency  shows  itself  not  only  in  the 
hand  but  in  the  whole  attitude.  One  is  the  attitude  of 
attraction;  the  other  is  the  attitude  of  aversion  or  re- 
jection. The  direction  of  the  movement  may  be  changed 
by  a  slight  change  in  the  mode  of  stimulation. 

To  make  this  test  accurately,  one  should  use  an  auto- 
matograph,  which  may  be  made  very  simply.  It  con- 
sists of  a  small  board  suspended  from  the  ceiling  as  a 
suitable  free  support  for  the  hand.  A  small  weighted 
pencil  is  placed  inside  a  tube  through  the  board  so  that 
it  traces  the  movements  of  the  board  upon  a  sheet  of 
paper  laid  upon  a  pane  of  glass.     This  is  exactly  the 


AFFECTIVE  TONE  203 

same  principle  as  that  used  in  so-called  spirit-writing 
by  Planchette  or  Ouijaboard.  These  latter  instruments 
convey  messages  which  may  be  entirely  unconscious  and 
involuntary  on  the  part  of  the  writer  and  still  possess 
coherence  and  relevancy.  The  odor  experiment  above 
is  just  as  truly  spirit-writing  as  these  messages,  only 
it  is  very  much  simpler  than  the  mediumistic  per- 
formances. 

The  expression  of  affective  tone  in  strength  tests  may 
be  demonstrated  very  simply.  The  person  experi- 
mented upon  is  required  to  pull  against  a  spring  which 
has  a  mechanism  for  graphic  tracing  of  the  force  of  the 
pull.  He  is  required  to  pull  as  hard  as  he  can  for 
fifteen  seconds ;  five  seconds  after  he  has  started  to  pull, 
he  is  given  a  whiff  of  odor  (or  stimulus  through  any 
other  sense)  and,  if  the  odor  is  agreeable,  the  tracing- 
point  will  rise,  showing  an  increase  in  the  strength  of 
pull,  whereas,  if  the  odor  is  disagreeable,  the  tracing- 
point  will  fall,  indicating  a  certain  amount  of  falling 
off  in  the  strength  of  pull. 

We  are  stronger  when  we  are  under  the  influence  of 
agreeable  stimuli  than  when  under  disagreeable  stimuli. 
The  modern  manufacturer  takes  advantage  of  this 
principle.  He  gives  his  workmen  encouragement  and 
agreeable  surroundings,  and  finds  that  they  are  stronger 
for  it. 

We  can  tell  by  the  attitude  and  expression  of  the  face 
of  a  man  whether  he  is  happy  or  sad,  proud  or  humble, 
courageous  or  cowardly,  etc.  These  differences  may  be 
stated  in  terms  of  muscular  tension,  circulation,  breath- 
ings relative  changes  in  the  volume  of  the  periphery  and 


204  AFFECTIVE  TONE 

the  brain,  etc.  But  very  little  work  of  permanent  value 
has  been  done  in  this  field  of  investigation. 

There  are  several  reasons  for  the  present  dearth  of 
experimental  studies  in  feeling.  The  processes  are 
extremely  elusive :  when  we  turn  in  upon  our  anger  to 
study  it,  the  anger  disappears.  The  feelings  are  not 
correlated  directly  with  traceable  objective  conditions 
as  sensations  are.  The  feelings  are  so  diffused  and  com- 
plex that  it  is  difficult  to  obtain  and  control  simple  con- 
ditions. The  term  feeling  is  used  in  more  than  a  score 
of  sanctioned  meanings.  Theories  of  feeling  are  notori- 
ously numerous. 

The  order  of  experiment  must  always  be  from  the 
simple  to  the  complex.  It  would  be  interesting  to  ex- 
periment on  love,  hatred,  fright,  ecstasy,  etc.,  but  hardly 
convenient,  or  discreet  at  the  present  stage.  Yet  we 
may  answer  many  of  the  fundamental  questions  of  com- 
plex and  strong  emotion  by  systematic  study  of  the 
simpler  forms. 


CHAPTER    XYI 
KEACTIOIsr-TIME 

For  the  Whole  Class* 
^^QuiCK  as  thought"  is  often  taken  to  mean  infinitely 
short  time,  or  no  time  at  all.  Yet  thinking  is  a  distress- 
ingly slow  process  with  some  of  ns.  A  century  and  a 
half  ago  a  distinguished  physiologist  estimated  that  the 
speed  of  the  nerve-impulse  was  about  57,600,000,000 
feet  per  second ;  a  century  later  it  was  measured  and 
found  to  be,  in  round  numbers,  100  feet  per  second.  It 
was  for  some  time  thought  to  have  a  speed  comparable 
with  the  speed  of  the  electric  current,  but  the  electric 
current  would  flash  half  the  distance  around  the  globe 
at  the  equator  while  a  nerve-impulse  passes  from  foot  to 
head  in  man.     The  conceptions  of  the  time  of  mental 

*  If  the  class  is  large,  it  may  be  divided  into  sections  of 
about  twelve  to  fifteen.  Select  a  conductor,  a  timer,  and  a  re- 
corder for  each  section  a  week  in  advance,  and  let  them  train 
themselves  so  that  they  are  prepared  to  conduct  the  experiment 
efficiently  and  economically.  The  conductor  shall  have  general 
command;  the  timer  shall  take  the  time  with  a  stop-watch;  the 
recorder  shall  take  full  notes.  The  conductor  and  the  recorder 
cannot  be  in  the  chain.  If  no  stop-watch  is  available,  the  timer 
must  also  be  out  of  the  chain  so  that  he  can  time  by  counting 
the  ticks  of  a  watch,  usually  fifths  of  a  second.  He  can  then 
count  by  groups  of  ten-fifths,  but  may  adapt  the  method  of 
counting  to  the  length  of  the  chain. 

The  experiment  may  be  performed  in  one  hour  if  proper  prep- 
arations have  been  made  and  the  reading  of  the  explanatory 
parts  is  postponed  until  the  experiments  have  been  completed. 

205 


206  REACTION-TIME 

processes  have  undergone  equally  great  revision  within 
the  same  period.  We  now  measure  the  duration  of 
mental  processes,  and  these  measurements  give  the 
mental  processes  concreteness  and  a  natural  setting. 
They  not  only  furnish  the  time  of  the  mental  act,  but  also 
serve  to  isolate  the  selected  process  and  make  it  tangible 
for  the  purpose  of  psychological  analysis  and  synthesis. 

The  term  reaction-time  is  used  to  denote  these 
measurements  because  it  is  customary  to  arrange  the 
experiment  so  that  the  termination  of  the  act  is  marked 
by  a  reaction."^ 

To  enable  the  whole  class  to  participate,  and  to  avoid 
the  use  of  elaborate  apparatus,  we  shall  adopt  the  chain- 
reaction  method.  The  class  forms  a  chain  and  a  given 
signal  is  passed  as  rapidly  as  possible  from  one  to  the 
next  until  it  has  completed  the  round.  The  total  time 
for  the  chain  is  divided  by  the  number  of  participants, 
which  apportions  the  average  individual  time  required 


*  *'A  great  variety  of  actions  may  be  viewed  as  responses  to 
stimuli.  There  is  a  flash  of  light,  and  we  wink;  a  burning  cinder 
falls  upon  the  hand,  and  we  draw  it  away;  a  bell  rings,  and  the 
engineer  starts  his  train,  or  the  servant  opens  the  door,  or  we 
go  down  to  dinner;  the  clock  strikes,  and  we  stop  work,  or  go  to 
keep  an  appointment.  Again,  in  such  an  occupation  as  copying, 
every  letter  or  word  seen  acts  as  a  stimulus,  to  which  the  written 
letter  or  word  is  the  response;  in  piano-playing,  and  the  guidance 
of  complicated  machinery,  we  see  more  elaborate  instances  of 
similar  processes.  The  printer  distributing  "pi",  the  post- 
office  clerk  sorting  the  mails,  are  illustrations  of  quick  forms 
of  reaction,  in  which  the  different  letters  of  the  alphabet  or  the 
different  addresses  of  the  mail  matter  act  as  the  stimuli,  and 
the  placing  them  in  their  appropriate  places  follows  as  the  re- 
sponse. In  many  games,  such  as  tennis  or  cricket,  the  various 
waj's  in  which  the  balls  are  seen  to  come  to  the  striker  are  the 
stimuli,  for  each  variation  of  which  there  is  a  precise  and  com- 
plex form  of  response  in  the  mode  of  returning  the  ball."  (Jaa- 
trow,  "The  Time-relations  of  Mental  Phenomena.") 


KEACTION-TIME  207 

for  the  act.  It  is  essential  that  all  should  understand 
clearly  what  the  act  is  and  what  attitude  to  take.  Exp. 
1  will  represent  simple  reactions;  all  the  following  ex- 
periments represent  complex  reactions.  It  is  in  the 
latter  that  we  measure  the  time  of  mental  processes  ac- 
cording to  the  plan  here  adopted. 

1.  Simple  Reaction,  a.  Visual — The  signal  shall 
be  the  quick  downward  movement  of  a  pencil,  and  this 
signal  shall  be  passed  as  rapidly  as  possible  from  one  to 
another.  Let  the  class  form  a  circle  and  face  away  from 
the  center.  At  the  conductor's  command  ^'Ready!", 
each  one  shall  raise  a  pencil  into  plain  view  of  the  per- 
son to  his  right ;  and,  about  three  seconds  after  the  con- 
ductor's warning  ^'Xow!",  the  timer  shall  simultane- 
ously start  the  stop-watch  and  give  the  signal  to  the 
person  at  his  right,  who  shall  in  turn  give  it  to  the  one 
at  his  right,  and  so  on,  the  signal  being  passed  as 
rapidly  as  possible  until  it  reaches  the  timer  again; 
and  he,  instead  of  passing  it  on,  shall  stop  the  stop- 
watch. 

In  this  and  each  of  the  following  experiments  make 
five  successive  trials ;  compute  the  average  of  the  five 
trials  and  divide  by  the  number  of  participants. 

h.  Auditory. — The  signal  shall  be  the  exclamation 
"Up !".  Let  all  keep  their  eyes  closed.  In  other 
respects  proceed  as  in  Exp.  1  a. 

c.  Tactual. — The  signal  shall  be  a  tap  on  the  right 
shoulder.  Let  each  one  turn  90°  to  the  right  and,  at 
the  conductor's  command  ^'Ready !",  place  the  tip  of  the 
index-finger  of  the  right  hand  so  that  it  all  but  touches 


208  KEACTION-TIME 

the  right  shoulder  of  the  person  in  front  of  him.  Let 
all  keep  their  eyes  closed.  In  other  respects  proceed 
as  in  Exp.  1  a. 

The  method  of  measurement  here  used  is  crude.  The 
time-measurement  is  not  fine  or  exact  enough;  the 
signal-response  is  too  indefinite ;  each  participant  labors 
under  different  conditions;  there  is  little  opportunity 
for  introspection;  the  practice  is  inadequate  and  there 
are  many  other  shortcomings.  Yet  the  experiment 
serves  very  well  to  bring  out  the  experience  of  time- 
relations. 

In  the  laboratory  the  exact  experiments  are  made  with 
chronoscopes  or  chronographs  which  measure  small  in- 
tervals of  time  accurately.  A  single  observer  is  isolated 
in  an  observation-room  from  which  all  disturbing  stimuli 
may  be  excluded.  The  signal  and  the  response  are 
simplified  and  made  more  exact.  The  observer  is 
trained,  numerous  trials  are  made,  the  variability 
of  the  records  is  computed,  the  reaction  is  fraction- 
ated *  for  the  purpose  of  the  introspection,  and  the 
conditions  may  be  controlled  and  regulated  in  great 
detail. 

These  "simple  reactions"  may  be  reduced  to  their 
component  parts  and,  under  certain  conditions,  the  time 
of  each  of  these  components  may  be  measured.  The 
complexity  of  the  process  becomes  apparent  wdien  we 
attempt  to  trace  the  physical  and  the  mental  steps  in  the 
act  as  in  the  following  outline. 


*  That  is,  the  observer  introspects  one  aspect  of  the  reaction  in 
one  set  of  experiments  and  then  repeats  the  experiment  and 
introspects  another  aspect,  etc. 


EEACTION-TIME  209 

THE   PHYSICAL  PROCESS  THE  MENTAL  PROCESS 

1.  The  response  of  the  sense-  1.  The  idea  of  the  signal  in 
organ  *    and    the    transmission       expectant  attention. 

of  the  nerve- impulse  to  the 
cortex  of  the  brain. 

2.  The   progress   of    this    im-  2.  The  perception  of  the  sig- 
pulse  through  the  cortex.                  nal,  the  association  of  the  sig- 
nal with  the  response,  and  the 
fiat  of  the  will  to  respond. 

3.  The  transmission  of  the  3.  The  idea  of  the  movement 
nerve-impulse  to  the  muscles,  followed  by  sensation  of  the 
the    response    of    the    muscles,       movement. 

and  the  transmission  of  sen- 
sory impulse  from  the  muscles 
to  the  cortex. 

The  very  incompleteness  and  arbitrariness  of  this  out- 
line serves  to  bring  out  the  complexity  of  the  act.  These 
three  steps  are  all  complex,  both  on  the  physical  and  the 
mental  sides.  The  real  reaction  consists  in  the  second 
step,  in  which  there  is  a  direct  correlation  between  the 
mental  and  the  neural  process.  So  far  as  the  mental 
act  is  concerned,  the  first  step  is  merely  a  preparation 
and  the  third  step  is  merely  a  consequence  of  the  reac- 
tion. Of  the  total  act,  the  reaction  proper  (the  second 
step)  occupies  but  a  small  portion  of  the  time.  There 
are  neural  processes  in  the  cortex  which  correspond  to 
all  three  steps  on  the  mental  side. 

Here,  then,  we  have  not  measured  the  time  of  the 
mental  act  of  reaction,  but  the  time  of  a  unique  set  of 
physical  and  mental  processes  in  which  the  conscious 


*The  transmission  of  the  sound-waves  through  the  ear  and 
their  conversion  into  a  nerve-impulse;  the  overcoming  of  the 
inertia  of  the  retina;  or  the  overcoming  of  the  inertia  of  the 
tactual  sense-organ. 


210  REACTION-TIME 

reaction  is  the  essential  element.  The  simple  reaction 
becomes  simpler  and  shorter,  as  well  as  more  uniform 
and  irresistible,  with  practice  ;  and  it  tends  to  be  less  and 
less  emphatic  in  consciousness  until  it  becomes  practi- 
tally  automatic.  All  this  is  implied  in  and  character- 
istic of  the  acquisition  of  skill  in  any  sort  of  activity. 
Skill  means  a  quick,  uniform,  appropriate,  and  but 
faintly  conscious  act. 

Life  is  a  series  of  reactions.  Therefore,  in  selecting 
some  of  these  for  experimentation,  w^e  may  have  great 
variety  in  conditions.  Among  the  principal  variables 
in  simple  reactions  are  the  following:  the  nature  of  the 
impression  or  signal,  the  strength  of  the  stimulus,  the 
mode  of  reaction,  the  direction  of  attention,  expectation, 
distraction,  degree  of  concentration,  practice,  fatigue, 
individual  differences,  mental  and  physical  state  of 
health,  the  influence  of  stimulants,  the  influence  of 
mental  encouragement  or  discouragement,  etc. 

Take  one  of  these,  the  direction  of  attention.  We 
find  three  characteristic  types  of  simple  reaction  with 
reference  to  this:  the  sensory,  in  which  attention  is 
directed  to  the  stimulus ;  the  motor,  in  which  attention  is 
directed  to  the  response ;  and  the  central,  in  which  at- 
tention is  not  focused  upon  either  stimulus  or  response 
exclusively,  but  is  allowed  to  oscillate  or  take  a  sort  of 
middle  ground.  The  motor  is  the  quickest  and  most 
effective  form,  and  there  is  a  tendency  to  pass  from  the 
other  types  to  this  with  practice.  It  may  become  so 
simple  as  to  be  purely  a  cerebral  reflex. 

Or  take  practice.  Practice  shortens  the  reaction-time 
so  rapidly  that  it  becomes  a  disturbing  factor  in  the 


■      REACTION-TIME  211 

present  experiments.  The  gain  by  practice  in  Exp.  1  c 
may  so  reduce  the  time  in  Exp.  2  that  the  additional 
factor  there  involved  may  not  show  appreciably  in  the 
time.  It  is  customary  to  distribute  the  practice  evenly 
among  trials  which  are  to  be  compared.  If  time  had 
permitted  it,  that  should  have  been  done  in  the  present 
experiments. 

2.  Discrimination. — The  signal  shall  be  a  tap,  as  in 
Exp.  1  c,  but  it  may  be  given  on  either  shoulder,  and  the 
person  touched  shall  respond  as  soon  as  he  knows  wdiich 
shoulder  was  touched,  but  he  must  determine  before- 
hand which  side  he  shall  touch ;  i.e.,  the  signal  shall  not 
determine  what  the  response  shall  be,  but  the  response 
shall  not  be  given  until  the  signal  has  been  distinguished 
as  a  right-side  or  a  left-side  signal.  Let  each  one  hold 
the  tip  of  a  finger  close  to  each  shoulder  of  the  person  in 
front  of  him.     In  other  respects  proceed  as  in  Exp.  1  c. 

This  act  involves  the  simple  reaction  to  touch  plus 
discrimination ;  to  get  the  discrimination-time,  subtract 
the  time  in  Exp.  1  c  from  the  time  in  this  experiment. 

3.  Choice. — The  signal  shall  be  a  tap  on  either 
shoulder,  as  in  Exp.  2,  but  the  response  must  be  made  on 
the  same  side  as  the  signal  is  received,  i.e.,  the  person 
touched  must  select  one  of  two  possible  responses  ac- 
cording to  directions  after  he  has  received  the  signal. 
In  other  respects  proceed  as  in  Exp.  2. 

This  act  involves  the  reaction  after  discrimination,  as 
in  Exp.  2,  plus  the  selective  choice ;  to  get  the  time  of 
the  choice,  subtract  the  time  in  Exp.  2  from  this. 

Discrimination  and  choice  are  common  acts  in  life. 


212  REACTION-TIME 

The  exj^eriments  might  have  been  varied  as  to  the  num- 
ber of  distinctions  or  choices,  the  degTee  of  similarity  of 
the  impressions,  the  specific  nature  of  the  impressions, 
foreknowledge  of  the  conditions,  adaptation  to  the 
individual,  etc. 

Discrimination  and  choice  are  clearly  mental  proc- 
esses. Exps.  2  and  3  illustrate  how  we  may  isolate  one 
process  after  another  for  the  measurement  of  its  dura- 
tion, for  introspection,  and  for  the  building  up  of  a 
complex  mental  act  of  which  the  elements  are  known 
and  under  control. 

4.  Cognition. — The  signal  shall  be  a  word,  and  the 
response  shall  be  another  word,  predetermined,  but 
spoken  only  as  soon  as  the  signal-word  has  been 
''cognized".  Each  response  becomes  the  sigiial  for  the 
next  person.     In  other  respects  proceed  as  in  Exp.  1  a. 

This  act  involves  reaction  after  cognition ;  to  get  the 
cognition-time,  subtract  the  simple  reaction  to  sound 
(1  h)  from  this. 

5.  Free  Association. — The  signal  shall  be  a  word, 
and  the  response  shall  be  another  word — the  first  word 
which  comes  to  mind  upon  hearing  the  signal.  Be  sure 
to  call  out  the  first  word  which  can  possibly  be  drawn 
from  the  imagery  suggested  by  the  signal- word ;  do  not 
stop  to  reason  or  discriminate.*  The  response  becomes 
the  signal  for  the  next,  and  so  on.  In  other  respects 
proceed  as  in  Exp.  4. 

*  As  in  the  experiments  on  the  laws  of  association,  it  is  all- 
important  that  the  response  shall  be  immediate  and  unreflective. 


KEACTION-TIME  213 

This  act  involves  simple  reaction,  cognition,  and  free 
association ;  to  get  the  time  of  the  free  association,  sub- 
tract the  time  in  Exp.  4  from  this. 

6.  Restricted  Association:  Memory. — The  signal 
shall  be  a  word,  and  the  response  shall  be  another  word 
which  begins  with  the  final  letter  of  the  signal.  The 
response  becomes  the  signal  for  the  next,  and  so  on.  In 
other  respects  proceed  as  in  Exp.  4. 

This  act  involves  simple  reaction,  cognition,  and  a 
partially  restricted  association;  to  get  the  time  of  this 
association,  subtract  the  time  in  Exp.  4  from  this. 

7.  Judgment. — The  signal  shall  be  the  naming  of  two 
edibles,  and  the  response  shall  be  the  naming  of  the  one 
of  these  two  which  is  preferred  and  one  other  edible 
thought  of  beforehand.  The  response  becomes  the 
signal  for  the  next,  and  so  on.  In  other  respects  proceed 
as  in  Exp.  4. 

To  get  the  time  of  judgment  proper,  measure  the 
time  of  simple  reaction  after  cognition  when  the  signal 
and  the  response  each  consist  of  two  words,  as  above,  and 
subtract  that  time  from  the  above  gross  time. 

What  have  we  measured  in  these  complex  reactions  ? 
We  have  measured  the  time  of  certain  purely  mental 
acts  of  discrimination,  choice,  cognition,  association, 
memory,  and  judgment. 

But  here  a  warning  and  qualification  is  necessary. 
Complex  mental  acts  are  not  made  up  of  simple  acts, 
each  butting  end  to  end  against  one  another  in  time. 
The  total  process  is  ordinarily  a  fusion  in  which,  how- 


214  KEACTION-TIME 

ever,  we  may  trace  essential  elements  or  movements. 
Thus,  although  the  mode  of  signaling  and  the  mode  of 
response  were  identical  in  Exps.  1  and  2,  it  is  not 
legitimate  to  assume  that  the  act  of  discrimination  was 
sandwiched  in  between  these  without  modifying  them, 
or  that  the  discrimination  folloAved  step  2  in  the  simple 
reaction  without  modifying  that  step.  The  act  of  dis- 
crimination gradually  fused,  on  the  one  hand,  with  the 
act  of  perception  of  the  signal  and,  on  the  other  hand, 
with  the  response.  The  perception-discrimination- 
response  became  one  act. 

The  process  of  elimination  which  we  have  followed 
therefore  does  some  violence  to  fact,  and  many  authori- 
ties prefer  not  to  use  it.  For  the  purpose  of  most 
psychological  measurements  the  time  of  the  total  com- 
plex act  is  quite  as  serviceable  as  the  time  of  an  isolated 
portion  of  the  act.  But  to  measure  the  time  of  a  mental 
process  strictly,  it  is  necessary  to  use  the  method  of 
elimination.  And  it  is  justified  provided  we  make  no 
superficial  assumptions  as  to  rigid  demarcations  between 
mental  components  of  an  act  and  adapt  the  method  to 
the  purpose  in  hand.  Even  allowing  for  a  reasonable 
amount  of  fusion  or  overlapping,  the  time-measurement 
cannot  be  far  from  right.  In  stating  a  measurement, 
the  fusion  is  taken  for  gi^anted.  But  it  is  literally  indis- 
putable, e.g.,  that  a  given  act  of  discrimination  united 
with  a  simple  reaction  lengthens  the  time  by  .06  sec. 

Someone  may  contend  that  these  are  all  purely 
physiological  processes  that  we  have  measured.  Para- 
doxical though  it  may  seem,  we  may  admit  the  correct- 
ness of  the  contention.     Modem  psychology  rests  upon 


EE  ACTION-TIME  215 

the  hypothesis  that  there  is  a  neural  process  parallel  to 
every  mental  process.  There  is  great  diversity  of 
opinion  as  to  the  nature  of  the  connection,  but  as  to  the 
fact  of  correlation  all  are  agreed.  If  we  are  capable  of 
thinking  of  these  processes  in  terms  of  neural  action,  it 
is  certainly  correct  and  legitimate  to  do  so.  Instead  of 
speaking  of  the  mental  acts  of  choice,  memory,  and  judg- 
ment, we  are  at  liberty  to  speak  of  these  acts  in  terms  of 
their  neural  concomitants.  But  what  do  we  know  about 
those  ?  Express  the  fact  of  judgment  in  terms  of  neural 
action  if  you  can !  Try  to  get  any  sort  of  crude  concep- 
tion of  it  and  you  fail.  The  thing  we  have  experienced, 
the  thing  we  know  most  concretely,  is  the  mental  act. 
The  fact  of  a  neural  concomitant  is  a  good  hypothesis, 
but  we  have  no  direct  knowledge  of  the  nature  of  that 
neural  process.  We  know  infinitely  more  of  the  mental 
than  of  the  physical:  and  the  mental  is  the  object  of 
interest  and  use,  the  physical  being  merely  a  condition ; 
hence  we  prefer  to  speak  in  terms  of  the  mental. 

All  the  mental  processes  here  studied  are  correlated 
with  the  neural  process  mentioned  in  step  2  of  the  out- 
line of  simple  reaction ;  there  is  only  a  difference  in  com- 
plexity. But  cerebral  physiology  and  physiological 
psychology  have  very  little  to  tell  us  in  the  way  of 
differentiation  or  description  of  these  central  processes. 

There  are  three  factors  in  the  customary  numerical 
records  of  reaction-measurements  which  are  often  of 
equal  if  not  greater  significance  than  the  average  time  of 
the  act.  These  are  the  mean  variation,  the  number 
and  kind  of  errors,  and  the  ^^mode.''  The  mean  varia- 
tion is  a  measure  of  the  reliability  of  the  measurement 


216  KEACTION-TIME 

and  the  imiformity  of  the  act,  and  the  errors  are  a 
measure  of  the  quality  of  the  work  done.  The  mode  is 
that  record  around  which  the  other  records  tend  to 
bunch ;  it  may  or  may  not  be  the  average.  If  a  series  of 
records  has  more  than  one  mode,  that  indicates  that 
there  is  some  disturbing  factor  in  the  measurement. 
The  four  factors  taken  together  may  measure  changes 
in  capacity  for  quickness,  uniformity,  and  reliability  of 
action. 

Knowledge  of  the  time  of  a  mental  process  is  in  itself 
of  little  value.  The  value  of  mental  chronometry  lies 
in  its  being  a  means  of  comparison.  But  the  time- 
measurement  becomes  a  sort  of  scale  or  foot-rule  which 
may  be  employed  in  a  great  variety  of  ways.  It  has 
probably  been  used  more  than  any  other  mode  of 
measurement  of  its  class  in  psychology.  Indeed,  in  the 
early  period  of  experimental  psychology,  persons  would 
ask  if  experimental  psychology  had  anything  but  reac- 
tion-experiments to  offer. 

It  may  be  employed  to  measure  certain  changes  in 
capacity,  such  as  the  effect  upon  mental  capacity  of 
drugs,  different  types  of  exercise,  rest,  practice,  fatigue, 
effort,  mental  encouragement,  health,  ideational  type, 
etc.  One  method  of  studying  fatigue  may  serve  to 
illustrate  this  class  of  applications.  The  experiment 
may  be  so  arranged  that  an  individual  engages  in  a  chain 
of  reactions.  Each  response  brings  out  the  sig-nal  for 
the  next.  He  must  work  at  maximum  speed  and  with- 
out interruption  for  a  long  period,  say  one,  two,  or  three 
hours.  The  reaction  is  the  work  which  fatigues,  and 
the  continuous  graphic  record  of  the  whole  series  of  re- 


REACTION-TIME  21 V 

action-times  contains  the  measure  of  capacity  for  this 
particular  work  under  various  stages  of  fatigue.  The 
average  time  in  a  given  minute  is  the  measure  of  the 
alertness,  the  mean  variation  of  the  reaction-times  dur- 
ing the  same  period  is  a  measure  of  the  power  of  applica- 
tion, and  the  record  of  the  number  and  kind  of  errors  is 
a  measure  of  the  quality  of  the  work  done. 

It  may  be  used  in  the  comparison  of  groups  of  indi- 
viduals for  statistical,  anthropological,  educational,  com- 
mercial, and  other  purposes.  It  then  shows  the  mini- 
mum time,  the  variability,  and  the  quality  of  any  act  on 
which  we  may  make  the  comparison.  Do  women 
ordinarily  form  quicker  judgments  than  men  in  a  given 
situation  ?  In  either  case,  which  is  the  more  likely  to 
be  right?  How  does  readiness  in  form-discrimination 
vary  with  age,  sex,  intelligence,  race,  type  of  high-school 
training,  etc.  ?  What  element  in  form  is  it  that  gives 
one  sprinter  the  advantage  over  another  in  the  start? 
Which  of  several  candidates  has  the  best  natural  ability 
for  bank-teller?  Such  are  some  of  the  questions  that 
may  be  solved  by  appropriate  reaction-measurements. 

It  may  be  used  as  a  measure  of  discernible  differences 
in  any  of  the  senses ;  e.g.,  to  determine  which  one  of  two 
or  more  grays  differs  most  from  a  given  standard  gray. 
It  has  been  of  good  service  in  determining  the  relative 
legibility  of  different  kinds  of  printing-type.  It  may 
be  used  as  a  means  of  determining  individual  peculiar- 
ities in  imagery,  in  working  out  laws  of  association  and 
memory,  in  studying  manifestations  of  the  subconscious, 
etc.  The  controlled  conditions  which  it  demands  are 
most  favorable  to  a  close  and  intimate  view  of  the  inter- 


218  REACTION-TIME 

relations  of  elements  in  a  complex  act.  And  it  is  not 
without  value  as  a  rigid  discipline  in  practical  exercises 
for  the  development  of  keenness  in  perception,  memory, 
reasoning,  and  action. 

Historically,  interest  in  the  reaction-measurement  has 
passed  through  several  phases.  It  began  over  a  hundred 
years  ago  in  the  study  of  the  personal  equation  of 
astronomers.  Then  the  physiologists  became  interested 
in  the  measurement  of  the  speed  of  the  nerve-impulse 
by  this  method.  This  roused  the  psychologists  to  the 
measurement  of  the  time  of  mental  processes.  At  the 
present  time  the  interest  of  the  psychologists  centers 
upon  its  use  as  an  aid  in  the  analysis  and  synthesis  of 
action. 


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